THE 



CHEHISTRY OF SOILS 

AND 



j SS Se ammm 



SNYDER 







LIBRARY OF CONGRESS. 

Chap....c:.. Copyright No. 

Shelf.:iD.Al 



UNITED STATES OF AMERICA. 



THE CHEMISTRY 



OP 



SOILS AND FERTILIZERS 



BY 



HARRY SNYDER, B.S., 

Professor of Agricultural Chemistry, University of Minnesota, 

and Chemist of the Minnesota Agricultural 

Experiment Station. 



EASTON, PA.: 
THE CHEMICAL PUBLISHING COMFAW, 

1899. 

{All rights reserved.) 



38465 



Copyright, 1S99, by Edward Hart. 



WO COP If a Ntu^. 




r " 






PREFACE 

For se\'eral years courses of instruction have been 
given at the University of Minnesota to classes of 
young men who intend to become farmers and who 
desire information that will be of assistance to them 
in their profession. In giving this instruction mimeo- 
graphed notes have been prepared, but the increase in 
the number of students and the volume of notes have 
necessitated the publication of this work. In its prep- 
aration, it has been the aim to give, in condensed form, 
the principles of chemistry which have a bearing upon 
the conservation of soil fertility and the economic use 
of manures. 

Harry Snyder. 
University of Minnesota, 

COI^I^EGE OF AGRICUI^TURE, 

St. Anthony Park, Minn. 
April /J, iSgg. 



CONTENTS 



INTRODUCTION 

Early uses of manures and the explanation of their action by the 
alchemists ; Investigations prior to 1800 ; Work of De Saussure, 
Davy, Thaer, and Boussingault ; Liebig's writings and their influ- 
ence ; Investigations of Lawes and Gilbert ; Contributions of 
other investigators ; Agronomy. Pages 1-9. 

CHAPTER I 

Physical Properties of Soils. — Chemical and physical properties 
of soils considered ; Weight of soils ; Size of soil particles ; Clay ; 
Sand ; Silt ; Form of soil particles ; Number and arrangement of 

soil particles ; Mechanical analysis of soils. Soil t3'pes 

Potato and truck soils ; Fruit soils ; Corn soils ; Medium grass and 
grain soils; Wheat soils. Relation of the soil to water ; Amount of 
water required for crops ; Bottom water ; Capillary water ; Hydro- 
scopic water; Loss of water by percolation, evaporation, and 
transpiration ; Influence of cultivation upon the water supply of 
crops ; Capillar}^ water and cultivation ; Shallow surface cultiva- 
tion ; Cultivation after rains ; Rolling; Sub-soiling; Fall plowino- ; 
Spring plowdng; Mulching; Depth of plowing; FertiHzers and 
their influence upon moisture content of soils ; Farm manures and 
soil moisture ; Permeability of soils ; Drainage ; Relation of soils to 
heat ; Heat from chemical reactions within the soil ; Heat and crop 
growth ; Color of soils ; Odor and taste of soils ; Relation of 
soils to electricity ; Importance of physical properties of the soil. 
Pages 9-48. 

CHAPTER II 

Geological Formation and Classification of Soils. — Geological 
study of soils ; Formation of soils ; Action of heat and cold ; 
Action of water ; Glacial action ; Chemical action of water ; Ac- 



vi CONTENTS 

tion of air and gases ; Action of vegetation and micro-organisms ; 
Distribution of soils ; Sedentary and transported soils ; Rocks 
and minerals from which soils are derived as quartz, feldspar, mica, 
hornblende, zeolites, granite, apatite, kaolin, limestone, gypsum ; 
Chemical composition of rocks. Pages 49-59. 

CHAPTER III 

Chemical Composition of Soils. — Elements combine to form 
minerals ; Classification of elements ; Combination of elements ; 
Forms in which elements are present in soils ; Acid-forming ele- 
ments, silicon, double silicates, carbon, sulphur, chlorine, phos- 
phorus, nitrogen, oxygen, hydrogen ; Base-forming elements, alu- 
minum, potassium, calciuni, magnesium, sodium, iron ; Classifica- 
tion of elements for plant-food purposes; Amount of plant food in 
different forms in various types of soils ; How a soil analysis is 
made ; Value of soil analysis ; Interpretation of the results of soil 
analysis ; Use of dilute acids as solvents in soil analysis; Distribu- 
tion of plant food in the soil ; Composition of typical soils ; 
"Alkali" soils and their improvement; Organic compounds 
of soil ; Sources ; Classification ; Humus ; Humates ; Humification ; 
Humates produced by different kinds of organic matter ; Value 
of humates as plant food, amount of plant food in humic forms ; 
Loss of humus by forest fires, by prairie fires, by cultivation ; 
Humic acid ; Soils in need of humus ; Soils not in need of humus ; 
Composition of humus from old and new soils ; Influence of different 
methods of farming upon humus. Pages 60-101. 

CHAPTER IV 

Nitrogen of the Soil and Air, Nitrification and Nitrogenous Ma- 
nures. — Importance of nitrogen as plant food ; Atmospheric 
nitrogen as a source of plant food. Experiments of Boussingault, 
Ville, and Lawes and Gilbert ; Result of field trials ; Experiments 
of Hellriegel and Wilfarth and recent investigators ; Composition 
of root nodules ; Amount of nitrogen returned to soil by leguminous 
crops and importance to agriculture ; Nitrogenous compounds 
of the soil ; Origin ; Organic nitrogen ; Amount of nitrogen in soils ; 
Removed in crops ; Nitrates and nitrites ; Ammonium compounds ; 



CONTENTS vn 

Ammonia in rain and drain waters ; Ratio of nitrogen to carbon in 
the soil ; I^osses of nitrogen from soils ; Gains of nitrogen to soils ; 
Nitrification ; Former views regarding ; Workings of an organism ; 
Conditions necessary for nitrification ; Influence of cultivation 
upon these conditions ; Nitrous acid organisms, ammonia-produ- 
cing organisms, denitrification, number and kind of organisms in 
soils ; Inoculation of soils with organisms ; Chemical products pro- 
duced by organisms ; Losses of nitrogen by fallowing rich prairie 
lands ; Deep and shallow plowing and nitrification ; Spring and 
fall plowing and nitrification ; Nitrogenous manures ; Sources ; 
Dried blood, tankage, flesh meal, fish scrap, seed residue, and uses 
of each ; Leather, wool waste, and hair ; Peat and muck ; Legumi- 
nous crops as nitrogenous fertilizers ; Sodium nitrate, ammonium 
salts ; Cost and value of nitrogenous fertilizers. Pages 102-137. 

CHAPTER V 

Fixation. — Fixation a chemical change, examples of; Due to 
zeolites ; Humus and fixation ; Other compounds of soil cause fixa- 
tion ; Soils possess different powers of fixation ; Nitrates do not 
undergo fixation ; Fixation of phosphates ; Fixation a desirable 
property of soils ; Fixation and the action of manures. Pages 138- 
140. 

CHAPTER VI 

Farm Manures. — Variable composition of farm manures ; Factors 
which influence composition of manures ; Absorbents ; Relation of 
food consumed to manures produced ; Bulky and concentrated 
foods ; Course of the nitrogen of the food during digestion ; Com- 
position of liquid and solid excrements ; Manurial value of foods ; 
Commercial valuation of manure ; Influence of age and kind of 
animal ; Manure from 3'oung and old animals ; Cow manure ; 
Horse manure ; Sheep manure ; Hog manure ; Hen manure ; Mix- 
ing manures ; Volatile products from manure ; Human excrements ; 
Preservation of manures ; Leaching ; Losses by fermentation ; 
Different kinds of fermentation ; Water necessary for fermenta- 
tion ; Composting manures ; Uses of preservatives ; Manure pro- 
duced in sheds ; Use of manures ; Direct hauling to field ; 
Coarse manures may be injurious ; Manuring pasture land ; Small 



Vlll CONTENTS 

piles of manure in fields objectionable ; Rate of application ; Most 
suitable crops to apply to ; Comparative value of manure and food ; 
Comparative value of good and poor manure ; Summary of wa3-s in 
which manures may be beneficial. Pages 141-171. 

CHAPTER VII 

Phosphate Fertilizers. — Importance of phosphorus as plant food ; 
Amount of phosphoric acid in soils, amount removed in crops ; 
Source of soil phosphoric acid ; Commercial forms of phosphoric 
acid ; Phosphate rock ; Calcium phosphates ; Reverted phosphoric 
acid ; Available phosphoric acid ; Manufacture of phosphate fertil- 
izers, acid phosphates, superphosphates ; Commercial value of 
phosphoric acid ; Basic slag phosphates ; Guano ; Bones ; Steamed 
bone ; Dissolved bone ; Bone black ; Use of phosphate fertilizers ; 
How to keep the phosphoric acid of the soil available. Pages 172- 
185. 

CHAPTER VIII 

Potash Fertilizers. — Potassium an essential element ; Amount of 
potash removed in crops ; Amount in soils ; Source of soil potash ; 
Commercial forms of potash ; Stassfurt salts, occurrence of ; 
Kainit ; Sulphate of potash ; Other Stassfurt salts ; Wood ashes, 
composition of ; Amount of ash in different kinds of wood ; Action 
of ashes on soils ; Leached ashes ; The alkalinity of ashes ; Coal 
ashes ; Miscellaneous ashes ; Commercial value of potash ; Use of 
potash fertilizers ; Joint use of potash and lime. Pages 186-195. 

CHAPTER IX 

Lime and Miscellaneous Fertilizers. — Calcium an essential ele- 
ment ; Amount of lime removed in crops ; Amount of lime in soils ; 
Different kinds of lime fertilizers ; Their physical and chemical 
action ; Action of lime upon organic matter and correcting acidity 
of soils ; Lime liberates potash ; Aids nitrification ; Action of land 
plaster on some "alkali" soils; Quicklime and slaked lime ; 
Marl ; Physical action of lime ; Judicious use of lime ; Miscel- 
laneous fertilizers ; Salt and its action on the soil ; Magnesium 
salts ; Soot ; Sea-weed ; Strand plants ; Wool washings. Pages 
196-204. 



CONTENTS IX 

CHAPTER X. 

Commercial Fertilizers. — History of development of industry ; 
Complete fertilizers and amendments ; Variable composition of 
commercial fertilizers ; Preparation of fertilizers ; Inert forms 
of matter in fertilizers; Inspection of fertilizers; Mechanical 
condition of fertilizers ; Forms of nitrogen, phosphoric acid, 
and potash in commercial fertilizers ; Misleading statements on 
fertilizer bags ; Estimating the valne of a fertilizer ; Home mixing ; 
Fertilizers and tillage ; Abuse of commercial fertilizers ; Proper 
use of ; Field tests ; General principles ; Preliminary experiments ; 
Verifying results ; Deficiency of one element ; Deficiency of two 
elements ; Will it pay to use fertilizers ? Amount to use per acre ; 
Influence of excessive applications ; Fertilizing special crops ; Com- 
mercial fertilizers and farm manures. Pages 205-224. 

CHAPTER XI. 

Food Requirements of Crops. — Amount of fertility removed by 
crops ; Assimilative powers of crops compared ; Way in which 
plants obtain their food ; Cereal crops ; General food requirements ; 
Wheat ; Barley ; Oats ; Corn ; Miscellaneous crops ; Flax ; Pota- 
toes ; Sugar-beets ; Roots ; Turnips ; Rape ; Buckwheat ; Cotton ; 
Hops ; Hay and grass crops ; Leguminous crops. Pages 225-237. 

CHAPTER XII. 

Rotation of Crops. — Object of rotating crops ; Principles involved 
in crop rotation ; Deep and shallow rooted crops ; Humus-consu- 
ming and humus-producing crops ; Crop residues ; Nitrogen-consu- 
ming and nitrogen-producing crops ; Rotation and mechanical 
condition of soil ; Economic use of soil water ; Rotation and farm 
labor ; Economic use of manures ; Salable crops ; Rotations advan- 
tageous in other ways ; Long- and short-course rotations ; Problems 
in rotations ; Conservation of fertility ; Necessity of manures ; 
Uses of crops ; Losses of fertility with different methods of farming ; 
Problems on income and outgo of fertility from farm. Pages 238- 
254- 

References ; Experiments ; Review Questions ; Corrections. 
Pages 255-272. 



THE CHEMISTRY OF 

SOILS AND FERTILIZERS 



INTRODUCTION 

Prior to 1800 but little was known of the sources 
and importance of plant food. Manures had been 
used from the earliest times, and their value was rec- 
ognized, but the fundamental principles underlying 
their use were not understood. It was believed that 
they acted in some mysterious way. The alchemists 
had advanced various views regarding theii action ; 
one was that the so-called "spirits'' left the decaying 
manure and entered the plant, producing more vigor- 
ous growth. As evidence, the worthless character of 
leached manure was cited. It was believed that the 
spirits had left such manure. The terms 'spirits of 
hartshorn', 'spirits of niter', 'spirits of turpentine', and 
many others reflect these ideas regarding the compo- 
sition of matter. 

Before the composition of plant and animal bodies 
was established, it was believed that one substance, 
like copper, could be changed to another substance, as 
gold. Plants were supposed to be water transmuted 



2 SOILS AND FERTILIZERS 

in some mysterious way directly into plant tissue. Van 
Helmont, in the seventeenth century, attempted to 
prove this. " He took a large earthen vessel and filled 
it with 200 pounds of dried earth. In it he planted a 
wallow weighing five pounds, which he duly watered 
wdth rain and distilled water. After five years he 
pulled up the willow and it now weighed one hundred 
and sixty-nine pounds and three ounces."' He con- 
cluded that 164 pounds of roots, bark, leaves, and 
branches had been produced b}' the direct transmuta- 
tion of the water. 

It is evident from the preceding example that aii}-- 
thing like an adequate idea of the growth and compo- 
sition of plant bodies could not be gained until the 
composition of air and water were established. 

The discovery of oxygen by Priestley in 1774, 
of the composition of water by Cavendish in 
1 781, and of the role which carbon dioxide plays in 
plant and animal life by DeSaussure and others in 
1800, form the nucleus of our present knowledge re- 
garding the sources of matter stored up in plants. It 
was from 1760 to 1800 that alchemy lost its grip and 
the way was prepared for the development of modern 
chemistry. 

The work of DeSaussure, entitled "Recherches 
sur la Vegetation," published in 1804, was the first 
systematic work showing the sources of the com- 
pounds stored up in plant bodies. He demonstrated, 



INTRODUCTION 3 

quantitatively, that the increase in the amount of 
carbon, hydrogen, and oxygen, when plants weie ex- 
posed to sunlight, was at the expense of the carbon 
dioxide of the air, and of the water of the soil. He 
also maintained that the mineral elements derived 
from the soil were essential for plant growth, and gave 
the results of the analyses of many plant ashes. He 
believed that the nitrogen of the soil was the main 
source of the nitrogen found in plants. These views 
have since been verified by many investigators, and 
are substantially those held at the present time re- 
garding the fundamental principles of plant growth. 
They were not, however, accepted as conclusive at 
the time, and it was not until nearly a half century 
later, when Boussingault, Liebig, and others repeated 
the investigations of DeSaussure, that they were 
finally accepted by chemists and botanists. 

From the time of DeSaussure to 1835, scientific 
experiments relating to plant growth were not actively 
prosecuted, but the scientific facts which had accumu- 
lated were studied and attempts were made to apply 
the results to actual practice. Among the first to see 
the relation between chemistry and agriculture was 
Sir Humphry Davy. In 181 3 he published his 
" Essentials of Agricultural Chemistry", which treated 
of the composition of air, soil, manures, plants, and 
of the influence of light and heat upon plant growth. 
About this same period, Thaer published an important 



4 SOILS AND FERTILIZERS 

work entitled " Principes Raisonnes d' Agriculture". 
Thaer believed that humus determined the fertility of 
the soil, that plants obtained their food mainly from 
humus, and that the carbon compounds of plants 
were produced from the organic carbon compounds of 
the soil. This gave rise to the so-called humus theory, 
which was later shown to be an inaccurate idea re- 
garding the source of plant food. The writings of 
Thaer were of a most practical nature, and they did 
much to stimulate later investigations. 

About 1830 there was a renewed interest in scientific 
investigations relating to agriculture. At this time 
Boussingault became actively engaged in agricul- 
tural research. He was the first to establish a chemical 
laboratory upon a farm and to make practical inves- 
tigations in connection with agriculture. This marks 
the establishment of the first agricultural experi- 
ment station. Boussingault's work upon the as- 
similation of the free nitrogen of the air is reviewed 
in Chapter IV. His study of the rotation of crops 
was a valuable contribution to agricultural science. 
He discovered many important facts relating to the 
chemical characteristics of foods, and was the first to 
make a comparative study of the amount of nitrogen 
in different kinds of foods and to determine the value 
of foods on the basis of the nitrogen content. His 
study of the production of saltpeter did much to pre- 
pare the way for later work on nitrification. The 



INTRODUCTION 5 

work of Boussingault covered a variety of subjects re- 
lating to plant growth. He repeated and verified 
much of the earlier work of DeSaussure, and also 
secured many additional facts relating to the chemis- 
try of crop growth. As to the source of nitrogen in 
crops, he states that : "The soil furnishes the crops 
with mineral alkaline substances, provides them with 
nitroofen, bv ammonia and bv nitrates, which are 
formed in the soil at the expense of the nitrogenous 
matters contained in diluvium, which is the basis of 
vegetable earth ; compounds in which nitrogen exists 
in stable combination, only becoming fertilizing by 
the effect of time." As for the absorption of the gas- 
eous nitrogen of the air by vegetable earth, he sa}'s : 
" I am not acquainted with a single irreproachable ob- 
servation that establishes it ; not onlv does the earth 
not absorb gaseous nitrogen, but it gives it off."^ 

The investigations of DeSaussure and Boussingault, 
and the writings of Davy, Thaer, Sprengel, and Schiib- 
ler prepared the way for the work and writings of 
Liebig. In 1840 he published "Organic Chemistry 
in its Applications to Agriculture and PliA'siology". 
Liebig's agricultural investigations were preceded by 
many valuable discoveries in organic chemistry, which 
he applied directly in his interpretations of agricul- 
tural problems. His waitings were of a forcible char- 
acter and were extremely argumentative. They pro- 
voked, as he intended, vigorous discussions upon 



6 SOILS AND FERTILIZERS 

agricultural problems. He assailed the humus theory 
of Thaer, and showed that humus was not an adequate 
source of the plant's carbon. In the first edition of 
his work he showed that farms from which certain 
products were sold naturally became less productive, 
because of the loss of nitrogen. In a second edition 
he considered that the combined nitrogen of the air 
was sufficient for crop production. He overestimated 
the amount of ammonia in the air, and underestimated 
the value of the nitrogen in soils and manures. A 
study of the composition of plant-ashes led him to 
propose the mineral theory of plant nutrition. De- 
Saussure had shown that plants contained certain 
mineral elements, but he did not emphasize their im- 
portance as plant food. Liebig's writings on the com- 
position of plant-ash, and the importance of supplying 
crops with mineral food led to the commercial prepara- 
tion of manures, which in later years has developed 
into the commercial fertilizer industry. The work of 
Liebig was not conducted in connection with field 
experiments. It had, however, a most stimulating 
influence upon investigations in agricultural chemistry, 
and to him we owe, in a great degree, the summari- 
zing of previous disconnected work and the mapping 
out of valuable lines for future investigations. 

Liebig's enthusiasm for agricultural investigations 
may be judged from the following extract : " I shall 
be happy if I succeed in attracting the attention of men 



INTRODUCTION y 

of science to subjects which so well merit to eneao-e 
their talents and energies. Perfect agriculture is the 
true foundation of trade and industry ; it is the foun- 
dation of the riches of states. But a rational system 
of agriculture cannot be formed without the applica- 
tion of scientific principles ; for such a system must be 
based on an exact acquaintance with the means of 
nutrition of vegetables, and with the influence of soils, 
and actions of manures upon them. This knowledge 
we must seek from chemistry, which teaches the mode 
of investigating the composition and of the study of 
the character of the different substances from which 
plants derive their nourishment. "3 

Soon after Liebig's first work appeared the investi- 
gations at Rothamsted by Sir J. B. Lawes were under- 
taken. The most extensive systematic work in both 
field experiments and laboratory investigations which 
have ever been conducted have been carried on by 
Lawes and Gilbert at Rothamsted, Eng. Dr. Gilbert 
had previously been a pupil of Liebig, and his associa- 
tion with Sir J. B. Lawes marked the establishment 
of the second experiment station. Many of the Roth- 
amsted experiments have been continued since 1844, 
and results of the greatest value to agriculture have 
been obtained. The investigations on the non-assimi- 
lation of the atmospheric nitrogen by crops, published 
in 1 861, were accepted as conclusive evidence upon 
this much-vexed question. The work on manures, 



8 SOILS AND FERTILIZERS 

nitrification, the nitrogen supply of crops, and on the 
increase and decrease of the nitrogen of the soil when 
different crops are produced, has had a most important 
bearing upon maintaining the fertility of soils. 

'' The general plan of the field experiments has been 
to grow some of the most important crops of rotation, 
each separately, for many years in succession on the 
same land, without manure, with farmyard manure, 
and with a great variety of chemical manures, the 
same kind of manure being, as a rule, applied year after 
year on the same plot. Experiments with different 
manures on the mixed herbage of permanent grass 
land, on the effects of fallow, and on the actual course 
of rotation without manure, and with different manures 
have likewise been made." "^ 

In addition to Davy, Thaer, DeSaussure, Bous- 
singault, Liebig, and Lawes and Gilbert, a great 
many others have contributed to our knowledge 
of the chemistry of soils. The work of Pasteur, while 
it did not directly relate to soils, indirectly had a great 
infiuence upon soil investigations. His researches 
upon fermentation made it possible for Schlosing to 
prove that nitrification was the result of the w^orkings 
of living organisms which have since been isolated 
and studied by Warington and Winogradsky. 

Many of the more recent investigations relating to 
the chemistry of soils are reviewed in the following 
chapters. Our knowledge regarding the chemistry, 



INTRODUCTION 9 

physics, geology, and bacteriology of soils is at the 
present time far from complete, but many facts have 
been discovered which are of the greatest value to the 
practical farmer. Of late years investigations relating 
to the chemistry of soils and fertilizers have become 
so extensive that the term 'agronomy' has been used 
to designate that part of agricultural chemistry. 

In soil investigations it has frequently happened, 
owing to imperfect interpretation of results and to 
the presence of many modifying influences, that the 
results and conclusions of one investigator appear to 
be directly contradictory to those of another. This 
is well illustrated in the investigations relating^ to the 
assimilation of the free atmospheric nitrogen, in which 
seemingly opposite conclusions now form a complete 
theory. 



CHAPTER I 

PHYSICAL PROPERTIES OF SOILS 

1. Soil. — Soil is disintegrated and pulverized rock 
mixed with animal and vegetable matter. The rock 
particles are of different kinds and sizes, and are in 
various stages of decomposition. If two soils are 
formed from the same kind of rock and differ only in 
the size of the particles, the difference is merely a 
physical one. If, however, one soil is formed largely 
from sandstone, while the other is formed from lime- 
stone, the difference is both physical and chemical. 
Hence it is that soils differ both physically and chem- 
ically. It is difficult to consider the physical proper- 
ties of a soil without also considering the chemical 
properties. The chemical and physical properties of 
a soil, when jointly considered, determine largely its 
agricultural value. 

2. Physical Properties Defined. — The physical 

properties of a soil are : 

1. Weight. 

2. Color. 

3. Size, form, and arrangement of the soil particles. 

4. The relation of the soil to water, heat, and cold. 

5. The relation of the soil to electricity. 

6. Odor and taste. 



PHYSICAL PROPERTIES OF SOILS n 

3. Weight. — Soils differ in weight according to 
the composition and size of the particles. Fine sandy 
soils weigh heaviest, while peaty soils are lightest in 
weight. But when saturated wdth water, a cubic foot 
of peaty soil weighs more than a cubic foot of sandy 
soil. Clay soils weigh less per cubic foot than sandy 
soils. The larger the amount of organic matter in a 
soil the less the weight. Pasture land, for exam- 
ple, weighs less per cubic foot than arable land. 
Weight is an important property to consider when the 
total amounts of plant food in two soils are compared. 
For example, a peaty soil containing i per cent, of 
nitrogen and weighing 30 pounds per cubic foot has 
less total nitrogen than a soil containing 0.40 per cent, 
of nitrogen and weighing 80 pounds per cubic foot. 

(i) The weight of soils per cubic foot is approxi- 
mately as follows : ^ 

Pouuds. 
Clay soil 70 to 75 

Fine sandy soil 95 to 1 10 

Loam soil 75 to 90 

Peaty soil 25 to 60 

Average prairie soil -r 

Uncultivated prairie soil 65 

Figures for the w^eight per cubic foot or specific 
gravity of soils are on the basis of the dry soil. When 
taken from the field the weight per cubic foot varies 
with the amount of water present. 

(2) The volume of a soil varies w^th the conditions 



12 SOILS ANI> FERTILIZERS » 

to which it has been subjected. Usually about 50 
per cent, of the volume of a soil is air space. A cubic 
foot of soil from a field which has been well cultivated 
weighs less than from a field where the soil has been 
compacted. Hence it is that soils have both a real 
and an apparent specific gravity. The apparent spe- 
cific gravity of a soil is sometimes less than half of the 
real specific gravity. The specific gravity of different 
soils as given by Shoen is as follows : ^ 

Specific gravity. 

Clay soil 2.65 

Sandy soil 2.67 

Fine soil 2.71 

Humus soil 2.53 

4. Size of the Soil Particles. — The size of the soil 
particles varies from those hardly distinguishable with 
the microscope to coarse rock fragments. The size of 
the particles determines the character of the soil as 
sandy, clay, or loam. The term ' fine earth ' is used to 
designate that part of the soil wdiich passes through a 
sieve with holes 0.5 mm. (0.02 inch) in diameter. 
Coarse sand particles and rock fragments which fail 
to pass through the sieve are called skeleton. The 
amount of fine earth and skeleton is variable. Arable 
soils, in general, contain from 5 to 20 per cent, of 
skeleton. 

The fine earth is composed of six grades of soil 
particles. The names and sizes are as follows : 



PHYSICAL PROPERTIES OF SOILS I3 

Millimeters. Inches. 

Medium sand 0.5 to 0.25 0.02 to o.oi 

Fine sand o. 25 to o. i o.oi to 0.004 

Very fine sand o. i to 0.05 0.004 to 0.002 

Silt 0.05 to O.OI 0.002 to 0.0004 

Fine silt o.oi to 0.005 0.0004 to 0.0002 

Clay 0.005 ^iid. less 0.0002 and less 

Soils are mechanical mixtures of various sized par- 
ticles. In most soils there is a predominance of one 
grade, as clay in heavy clay soils, and medium sand 
in sandy soils. No soil, however, is composed entirely 
of one grade. The clay particles are exceedingly 
small ; it would take 5000 of the larger ones, if laid 
in a line wath the edges touching, to measure an inch, 
w^hile it would take but 50 of the larger medium sand 
particles to measure an inch. 

5. Clay. — The term clay used physically denotes 
those soil particles less than 0.005 nin^- (0.0002 inch) 
in diameter, without regard to chemical composition. 
As used in a physical sense clay may be silica, feld- 
spar, limestone, mica, kaolin, or any other rock or 
mineral which has been pulverized until the particles 
are less than 0.005 ^^^- i^ diameter. Chemically, 
however, the term clay is restricted to one material, 
as wall be explained in another part of the work. 
The physical properties of clay are well knowm. It 
has the power of absorbing a large amount of water, 
and will remain suspended in water for a long time. 
The roiled appearance of many streams and lakes is 



14 SOILS AND FERTILIZERS 

due to the presence of suspended clay particles. The 
amount in agricultural soils may range from 3 to 50 
per cent. Clay soils, if worked when too wet, become 
puddled ; then percolation cannot take place, and the 
accumulated surface water must be removed by the 
slow process of evaporation. 

6. Silt. — The silt particles are, in size, between sand 
and clay. Many of the western prairie subsoils, clay- 
like in nature, are composed mainly of silt. The silt 
imparts characteristics intermediate to sand and clay. 
While a clay soil is nearly impervious to water, and 
when wet works with difficulty, a silt soil is more 
permeable, but is not as open and porous as a sandy 
soil. When a soil containing large amounts of clay 
and silt is treated with water, the silt settles slowly, 
while the clay remains in suspension. The fine de- 
posit in ditches and drains, where the water moves 
slowly, is mainly silt. 

7. Sand. — There are three grades of sand. The 
characteristics, as permeability and non-cohesion of 
particles, are so well known that they do not require 
discussion. A soil composed entirely of sand would 
have little, if any, agricultural value. Sandy soils 
usually contain from 5 to 15 per cent, of clay and 
silt. The relative sizes of sand, silt, and clay are given 
in the illustration. 

8. Form of Soil Particles. — Soil particles are ex- 



PHYSICAL PROPERTIES OF SOILS 



15 



tremely varied in form. When examined with the 
microscope they show the same diversity as is observed 
in larger stones. In some soils the particles are spher- 
ical, while in others they are angular. The shape 




Fig. I. Medium Sand X 150. Fig. 2. Fine Sand X 150. Fig. 3, 
Very Fine Sand X 150. Fig. 4. Silt X 3?5. Fig- 5- Fine Silt X 
325. Fig. 6. Clay X 325- 

of the particles is determined by the way in which the 
soil has been formed and also by the nature of the 
rock from which it was produced. 

The form and arrangement of the particles are im- 
portant factors to consider in dealing with the water 



l6 SOILS AND FERTILIZERS 

content of soils. In the wheat lands of the Red 
River Valley of the North, the particles are small and 
spherical, being formed largely from limestone rock, 
while the snbsoil of the western prairie regions is 
composed largely of angular silt particles, which are 
intermingled with clay, forming a mass containing 
only a minimum of inter soil spaces. The silt particles 
being angular and imbedded in the clay, the soil has 
more the character of clay than of silt. While these 
two soils are unlike in physical composition, the form 
and arrangement of the particles give each nearly the 
same water-holding power. On account of a differ- 
ence in the form and arrangement of the soil particles 
two soils may have the same mechanical composition, 
and yet possess materially different physical proper- 
ties. In some soils lo per cent, of clay is of more 
value agriculturally than in other soils. Ten per cent, 
of clay associated with 60 or 70 per cent, of silt, 
makes a good grain soil, while 10 per cent, of clay 
associated largely with sand makes a soil poorly suited 
to grain culture. 

The classification of the soil particles into sand, silt, 
and clay is purely an arbitrary one. Various authors 
use these terms in different ways, and when compar- 
ing soils, reported in different works, one may avoid 
confusion by omitting the names and noting only the 
sizes of the particles. A division has recently been 
suggested by Hopkins ^ iu which the square root is 



PHYSICAL PROPERTIES OF SOILS 1 7 

often taken as the constant ratio between the grades 
of soil particles. 

9. Number of Particles per Gram of Soil. — It has 

been estimated that a gram of soil contains from 
2,000,000,000 to 20,000,000,000 soil particles ; soils 
which contain less than 1,700,000,000 are unproduct- 
ive. The number of particles in a given volume of 
soil varies with their size and form. According to 
Whitney^ the number of particles per gram of differ- 
ent soil types is as follows : 

Early truck 1,955,000,000* 

Truck and small fruit • 3,955,000,000 

Tobacco 6,786,000,000 

Wheat 10,228,000,000 

Grass and wheat 14,735,000,000 

Limestone 19,638,000,000 

Assuming that the particles are all spheres, it is es- 
timated that in a cubic foot of soil a surface area of 
from two to three and one-half acres is presented to 
the action of the roots. 

1 . Methods Employed in Separating Soil Particles . 

— Sieves with circular holes 0.5, 0.25, and o. i mm. 
are employed for the purpose of separating the three 
coarser grades of sand. The sieve <7, 0.5 mm. size, is con- 
nected wnth the filtering flask c by means of the tube 
b^ and the flask is connected at point d with a suc- 
tion-pump. Ten grams of soil, after treatment with 

■■'•Figures below sixth place omitted and ciphers substituted. 



i8 



SDILS AND FERTILIZERS 



boiling water, are placed in the sieve. Water is passed 
through until the washings are clear. All particles 
larger than 0.5 mm. remain in the sieve, and after dry- 
ing and igniting, are weighed. The contents of flask r, 
containing the particles less than 0.5 mm., are then 
passed through a sieve having holes 0.25 mm. in 
diameter. Finally a o. 10 mm. diameter sieve is used. 
The fine sand and silt are separated by gravity. The 
fine sand with some silt and clay are read- 
ily deposited and the water containing 
the suspended clay is decanted into a 
second glass vessel. The residue is treated 
with more water and allowed to settle; 
this operation is repeated until the micro- 
scope shows the soil particles to be nearly 
all of one grade. 

Clay is obtained by 
evaporating an aliquot 
portion of the washings 
or by determining the 
total per cent, of the other grades of particles and the 
volatile matter and subtracting the sum from 100. 
This is the Osborne sedimentation method with modi- 
fications. 9 Hilgard's'° elutriator, and the apparatus 
of Shoen-Mayer are also used for separating the soil 
particles. 

SOIL TYPES 

II. Crop Growth and Physical Properties. —The 





Figs. 8 and 9. 



SOIL TYPES 19 

preference of certain crops for particular kinds of soil, 
as wheat for a clay subsoil, potatoes for a sandy soil, 
and corn for a silt soil, is due mainly to the peculiari- 
ties of the crop in requiring definite amounts of water, 
and a certain temperature for growth. These condi- 
tions are met by the soil being composed of various 
grades of particles which enable a certain amount of 
water to be retained, and the soil to properly respond 
to the influences of heat and cold. In considering 
soil types, it should be remembered that there are so 
many conditions influencing crop growth that the 
crop-producing power cannot always be determined by 
a mechanical analysis of the soil. The following 
types have been found to hold true in a large number 
of cases under average conditions, but they do not 
represent wdiat might be true of a case under special 
conditions. For example a sandy soil of good fer- 
tility in w^iich the bottom water is only a few feet 
from the surface, may produce larger grainc rops_than 
a clay soil in which the bottom water . is at a greater 
depth. In judging the character of a soil, special 
conditions must always be taken into consideration. 
In discussing the following soil types, a normal supply 
of plant food and an average rainfall are assumed in 
all cases. 

12. Potato and Early Truck Soils. — The better 
types of potato soils are those which contain about 60 
percent, of medium sand, 20 to 25 percent, of silt, and 



20 SOII.S AND FERTILIZERS 

about 5 per cent, of clay. Soils of this nature when 
supplied with about 3 per cent, of organic matter will 
contain from 5 to 12 per cent, of water. The best 
conditions for crop growth exist when the soil con- 
tains from 5 to 7 per cent, of water. In a sandy soil 
vegetation may reduce the water to a much lower 
point than in a clay soil. On account of sandy soil 
giving up its water so readily to growing crops nearly 
all is available, while on heavy clay, crops show the 
want of water when the soil contains from 7 to 8 per 
cent., because the clay holds the water so tenaciously. 
When potatoes are grown on soils where there is an 
abnormal amount of water the crop is slow in matur- 
ing. For early truck purposes in northern latitudes, 
sandy soils are the most suitable because they warm 
up more readily, and the absence of an abnormal 
amount of water results in early maturity. Excellent 
crops of potatoes are grown on many of the silt soils 
of the west which have a materially different com- 
position from the type given. A soil may have all 
of the requisites physically for the production of good 
potato and truck crops, and still be unproductive on 
account of some peculiarity in chemical composition. 

13. General Truck and Fruit Soils. — For fruit grow- 
ing and general truck purposes the soil should contain 
more clay and less sand than for early truck farming. 
Soils containing from 10 to 15 per cent, of clay and not 
more than 40 per cent, of sand are best suited for 



SOIL TYPES 21 

ofrowing: small fruits. Such soils will retain from lo 
to 1 8 per cent, of water. There is a noticeable differ- 
ence as to the adaptability of different kinds of fruit 
to different soils. Some fruits thrive on clay land, 
provided the proper cultivation and treatment are 
given. There is as much diversity of soil, required for 
producing different fruit crops as for the production of 
different farm crops. As a rule, however, a silt soil 
is most capable of being adapted to the various con- 
ditions required by fruit crops. 

14. Corn Soils. — The strongest types of corn soils 
are those which contain from 40 to 45 per cent, cf 
medium and fine sand and about 15 per cent, of clay. 
Corn lands should contain about 1 5 per cent, of avail- 
able water. Heavy clays produce corn crops which 
mature later than those grown on soils not so close 
in texture. Many corn soils contain less sand and 
clay, but more silt than the figures given. If the soil 
contains a high per cent, of organic matter, good corn 
crops may be produced where there is less than twelve 
per cent, of clay. Soils containing a high per cent, of 
sand are usually too deficient in available water to 
produce a good crop. On the other hand heavy clay 
soils are slow in warming up and are not suited to corn 
culture. 

The strongest types of corn soils have the proper 
mechanical composition for the production of good 
crops of sorghum, cotton, flax, and sugar-beets. How- 



22 SOILS AND FERTILIZERS 

ever, the amount of available plant food required for 
each crop is not the same. The western prairie soils 
which produce most of the corn raised in the United 
States, are composed largely of silt. 

15. Medium Grass and Grain Soils. — For the pro- 
duction of grass and grain a larger amount of water 
is required than for corn. The yield of both is de- 
termined largely by the amount of water which the 
soil contains. For an average rainfall of about 30 
inches, good grass and grain soils should contain 
about 15 per cent, of clay and 60 per cent, of silt. 
Such a soil ordinarily holds from 18 to 20 per cent, 
of water. Many grass and grain soils have less silt 
and more clay. A soil composed of about 30 per 
cent, each of fine sand, silt, and clay, would also be 
suitable, mechanically, for general grain production. 
There are a number of different types of grass and 
grain soils, with different proportional amounts of 
sand, silt, and clay. Silt soils, however, form the 
larger part of the grain soils of the United States. 

16. Wheat Soils. — For wheat production, soils of 
a closer texture are required than for general grain 
farming. There are three classes of wheat soils. The 
first (i in Fig. 10) contains from 30 to 50 per cent, of 
clay particles, these being mostly disintegrated lime- 
stone. The soil of the Red River Valley of the North 
belongs to the first class of wheat-producing soils. 
The surface soil contains from 8 to 12 percent, of veg- 



soil. TYPES 



23 



etable matter and the subsoil about 25 per cent, of 
limestone in a very fine state of division. For the 
production of wheat the subsoil should contain 20 per 
cent, of water. A crop can, however, be produced with 
less water, but a smaller vield is obtained. 



C/ac/ 




fine 





Fig. 10. Soil tj'pes. 



The second type of wheat soil (2 in Fig. 10) con- 
tains less clay and more silt. Many prairie subsoils 
w^hich produce good crops of wheat contain about 20 
per cent, of sand, 50 per cent, of silt, and from 20 to 
30 per cent, of clay. Soils of this class when w^ell 
stocked with moisture in the spring are capable of 



24 SOILS AND FERTILIZERS 

producing good crops of wheat, but are not able to 
withstand drought so well as soils of the first class. 

To the third class of wheat soils (3 in Fig. 10) belong 
those which are composed mainly of silt, containing 
usually 75 per cent., and from 10 to 15 per cent, of clay. 
The high per cent, of fine silt gives the soil clay-like 
properties. Soils of this class are adapted to a great 
variety of crops. For the production of wheat on silt 
vSoils it is very essential that a good supply of organic 
matter be kept in the soil so as to bind together the 
soil particles. The special peculiarities of the different 
grain crops as to soil requirements will be considered 
in connection with the food requirements of crops. 

17. Sandy, Clay, and Loam Soils. — In ordinary 
agricultural literature the term 'sandy,' 'clay,' or 
' loam ' is used to designate the prevailing character of 
the soil. Sandy soils usually contain 90 per cent, or 
more of silica or chemically pure sand. The term 
light sandy soil is sometimes used to indicate that the 
soil is easily worked, while the term heavy clay 
means that the soil offers great resistance to cultiva- 
tion. Many soils which are clay-like in character are 
not composed very largely of clay. There are sub- 
soils in the western states which have clay-like char- 
acteristics but contain only about 15 per cent, of clay, 
the larger part of the soil being silt. A loam soil is a 
mixture of sand and clay ; if clay predominates the 
soil is a clay loam, while if sand predominates it is a 
sandy loam. 



RELATION OF THE SOIL TO WATER 

i8. Amount of Water Required by Crops. — Ex- 
periments have shown that it takes from 275 to 375 
pounds of water to produce a pound of dry matter in 
a grain crop. In order to produce an average acre of 
wheat 350 tons of water are needed. The amount of 
water required for the production of an average acre 
of various crops is as follows : " 

Average amount. IMininiuni amount. 

Tons water. Tons water. 

Clover 400 310 

Potatoes 4C0 325 

Wheat 350 300 

Oats 375 300 . 

Peas 375 300 

Corn 300 

Grapes 375 

Sunflowers*^ 6ocxd 

The rainfall during the time of growth is frequently 
less than the amount of water required for the pro- 
duction of a crop. An average rainfall of 2 inches 
per month during the three months of crop growth 
would be equivalent to only 369 tons of water per 
acre, a variable part of which is lost by evaporation. 
Hence it is that the rainfall during an average grow- 
ing season is less than .the amount of water required, 
and in order to produce crops, the water stored up in 
the soil must be drawn upon to a considerable extent. 
Inasmuch as the soil's reserve supply of w^ater is such 
an important factor in crop production, it follows that 



26 SOILS AND FERTILIZERS 

the capacity of the soil for storing up water and giving 
it up as needed is a matter to be considered, par- 
ticularly since the power of the soil for absorbing 
and retaining water may be influenced by cultivation 
and manuring. Before discussing the influence of 
cultivation upon the soil water, the forms in which it 
is present in the soil should be studied. Water is 
present in soils in three forms : (i) bottom water, (2) 
capillary water, and (3) hydroscopic water. 

19. Bottom Water is water which stands in the soil 
at a general level, and fills all the spaces between the 
soil particles. Its distance from the surface can be 
told in a general way by the depth of surface w^ells. 
Bottom water is of service to growdng crops when it is 




Fig. II. Water films surrounding soil particles. 

at such a depth that it can be brought to the plant 
roots by capillarity, but when near the surface so that 
the roots are immersed, very poor conditions for crop 
growth exist. When the bottom water can be brought 
within reach of the roots by capillarity a crop 
has an almost inexhaustible supply. In many soils 
known as old lake bottoms such conditions exist. 



RELATION OF THE SOIL TO WATER 



27 



20. Capillary Water. — The water held in the 
capillary spaces above the bottom w^ater is known as 
the capillary water. The capillary spaces of the soil 
are the small spaces between the soil pa: tides in 
which water is held by surface tension ; that is, the 
force acting between the soil and the water is greater 
than the force of gravity. If a series of glass tubes of 
different diameters be placed in water it will be ob- 
served that in the smaller tubes water rises much 
higher than in the larger. The water rises in all of 



"^ 



Fig. 12. Comparative height to which water rises in glass tubes. 

the tubes until a point is reached where the force of 
gravity is equal to the force of surface-tension. In 
the smaller tubes surface-tension is greater than the 
force of gravity, and the water is drawn up into the 
tube. In the larger tubes the surface-tension is less 
and water is raised only a short distance. There 
are present in the soil many spaces which are capable 
of taking up water in the same way as the small glass 
tubes. The height to which water can be raised by 



28 SOILS AND FERTILIZERS 

capillarity depends upon the size and arrangement of 
the soil jDarticles. Water may be raised by capillarity 
to a height of several feet. Ordinarily, however, the 
capillary action of water is confined to a few feet. The 
arrangement of the soil particles influences greatly the 
capillary power of the soil. Usually from 30 to 60 per 
cent, of the bulk of a soil is air space : by compacting, 
the air spaces may be decreased ; by stirring, the air 
spaces are increased. In some soils of a close texture an 
increase in air spaces results in an increase of capillary 
spaces and of water-holding capacity, while in other 
soils, as coarse sandy soils, increasing the air spaces 
decreases the capillary spaces and the water-holding 
capacity. The best conditions for crop production 
exist when the soil contains water to the extent of 
about 40 per cent, of its total capacity of saturation. 

21. Hydroscopic Water. — By hydroscopic water is 
meant the water content of the soil atmosphere. The 
air which occupies the non-capillary spaces of the soil 
is charged with moisture in proportion to the water in 
the soil. Under normal conditions the soil atmos- 
phere is nearly saturated. When soils have exhausted 
their capillary water, the water in the soil atmosphere 
is correspondingly reduced. The available supply in 
other forms being exhausted, the hydroscopic water 
cannot contribute to plant growth. 

22. Loss of Water by Percolation. — Whenever a 
soil becomes saturated, percolation or a downward 



RELATION OF THE SOIL TO WATER 29 

movement of the water begins. The extent to which 
losses by percolation may occur depends upon the 
character of the soir and the amount of rainfall. 
When soils are covered with vegetation the losses by 
percolation are less than from barren fields. In all 
soils which have only a limited number of capillary 
spaces and a large number of non-capillary spaces, the 
amount of water which can be held above the bottom 
water is small. From such soils the losses by perco- 
lation are greater than from soils which have a larger 
number of capillary spaces, and a smaller number of 
non-capillary spaces. In coarse sandy soils many of 
the spaces are too large to be capillary. 

If all of the water which falls on some soils could be 
retained and not carried beyond the reach of crops by 
percolation, there would be an ample supply for agri- 
cultural purposes. To prevent losses by percolation, 
the texture of the soil may be changed by cultivation 
and by the use of manures. If the soil is of very fine 
texture, as a heavy clay, percolation is slow, and before 
the water has time to sink into the soil, evaporation 
begins; with good cultivation the water is able to 
penetrate to a depth beyond the immediate influence of 
evaporation. Compacting an open porous soil by 
rolling, checks rapid . percolation and prevents the 
water from being carried beyond the reach of plant 
roots. In order to prevent excessive losses by perco- 
lation, the treatment must be varied to suit the re- 
quirements of different soils. 



30 SOILS AND FERTILIZERS 

23. Loss of Water by Evaporation. — The factors 
which influence evaporation are temperature, humidity, 
and rate of movement of the air. When the air con- 
tains but little moisture and is heated and moving 
rapidly, the most favorable conditions for evaporation 
exist. In semiarid regions the losses of water by 
evaporation are much greater than by percolation. 
The dry air comes in contact with the soil, the soil 
atmosphere gives up its water, and, unless checked by 
cultivation, the subsoil water is brought to the surface 
by capillarity and lost. In porous soils, a greater 
freedom of movement of the air is possible, which in- 
creases the rate of evaporation. When the surface of 
the soil is covered with a layer of finely pulverized 
earth, or with a mulch, excessive losses by evaporation 
cannot take place, because a material of different tex- 
ture is interposed between the soil and the air. 

24. Loss of Water by Transpiration. — Losses of 
water may also occur from the leaves of plants by the 
process known as transpiration. Helriegel observed 
that during some years 100 pounds more water were 
required to produce a pound of dry matter than in 
other years, because of the difference in the amount of 
water lost by transpiration. The loss of water by 
evaporation can be controlled by cultivation, but the 
loss by transpiration can be only indirectly influ- 
enced. Hot dry wdnds may cause crops to wilt be- 
cause the water lost by transpiration exceeds the amount 
which the plant takes from the soil. 



INFLUENCE OF CULTIVATION 3 1 

The three ways in which crops are deprived of 
water are by (i) percolation, (2) evaporation, and (3) 
transpiration. With proper methods of cultivation, 
losses by percolation and evaporation may be controlled, 
and losses by transpiration may be reduced. 

INFLUENCE OF CULTIVATION UPON THE WATER SUPPLY 

OF CROPS 

25. Capillarity Influenced by Cultivation. — The 

capillarity of the soil is subject to change with different 
methods of cultivation, as rolling and subsoiling, deep 
plowing and shallow surface cultivation. The method of 
cultivation which a soil should receive in order to secure 
the best water supply for crops must vary with the 
rainfall, the nature of the soil, and the crop to be pro- 
duced. It frequently happens that the annual rainfall 
is sufficient to produce good crops, but is too unevenly 
distributed. It is possible, to a great extent, to vary 
the cultivation to meet the water requirements of 
crops. 

26. Shallow Surface Cultivation. — When shallow 
surface cultivation is practiced, the capillary spaces 
near the surface are destroyed and the direct connec- 
tion of the subsoil water w4th the surface is broken. 
When the soil particles have been disturbed and a layer 
of finely pulverized earth covers the surface, there is not 
that close contact which enables the water to pass 
from particle to particle. When evaporation takes 
place there is a movement of the subsoil water to the 



32 



SOILS AND FERTILIZERS 



surface, but if the surface is covered with a layer of 
fine earth, the subsoil water cannot readily pass 
through such a medium, and evaporation is checked. 
Hence shallow surface cultivation conserves the soil 
moisture. 

The means by which surface cultivation is accom- 
plished must, of necessity, vary with the nature of the 




Fig. 13. With surface cultivation, 

soil. If a harrow is used the pulverization should be 
complete. If a disk is used the teeth should be set at 
an angle, and not perpendicularly, so as to prevent, as 




Fig. 14. Without surface cultivation. 

suggested by King,^^ the formation of hard ridges 
which hasten evaporation. When the disk is set at an 
angle, a layer of soil is completely cut off, and the 
capillary connection with the subsoil is broken. Sur- 
face cultivation should be from two to three inches 



INFLUENCE OF CULTIVATION 33 

deep, and the finer the condition in which the surface 
soil is left, the better. 

Shallow surface cultivation should be resorted to as 
a means of conserving soil moisture. It can be prac- 
ticed in connection with deep plowing, shallow plow- 
ing, subsoiling, or rolling ; in fact, it can be combined 
with any method of preparing the land. Shallow sur- 
face cultivation does not mean that the soil should not 
be previously well prepared by thorough cultivation. 
The following example shows the extent to w^hich 
shallow surface cultivation may conserve the soil 
water. '3 

Per cent, of water in cornfield. 
With shallow sur- Without shallow 
face cultivation. surface cultivation. 

Soil, depth 3 to 9 inches 14. 12 8.02 

Soil, depth 9 to 15 inches 17.21 12.38 

27. Cultivation after a Rain. — When evaporation 
takes place immediately after a rain, not only is there 
a loss of the water which has fallen, but there may 
also be a loss of the subsoil water by translocation, if 
nothing be done to prevent." The following example 
shows the extent to which the subsoil water may be 
brought to the surface. '^ 

Per cent, of water. 
Surface soil. Subsoil. 

I to 3 inches. 6 to 12 inches. 

Before the shower 9.77 18.22 

After the shower 22.11 16.70 

The rainfall was sufficient to have raised the w^ater 
content of the surface soil to 20.77 per cent. The 
subsoil showed a loss of 1.52 per cent., while the sur- 



34 SOILS AND FERTILIZERS 

face soil showed a gain of 1.34 per cent, in addition to 
the water received from the shower. If evaporation 
begins before the equilibrium is reestablished, there is 
lost, not only the water from the shower, but also the 
water which has been translocated from the subsoil to 
the surface. Hence the importance of shallow surface 
cultivation immediately after a rain. 

When a subsoil contains a liberal supply of water, 
and the surface soil a minimum amount, there is after 
an ordinary shower a movement of the subsoil water 
to the surface. The soil particles at the surface are 
surrounded with films of water which thicken at the 
expense of the subsoil water. Surface-tension is the 
cause of this movement of the water to the surface, 
and under the conditions stated it is temporarily 
greater than the force of gravit}\ 

A thin hard crust should never be allowed to form 
after a rain, because it hastens the losses by evapora- 
tion, while a soil mulch formed by surface cultivation 
has the opposite effect. 

28. Rolling. — The use of heavy rollers for com- 
pacting the soil is beneficial in a dry season on a soil 
containing large proportions of sand and silt. Rolling 
the land compacts the soil and improves the capillary 
conditions, enabling more of the subsoil water to be 
brought to the surface. Experiments have shown 
that when land is rolled the amount of water in the 
surface soil is increased. This increase is, however, 



INFLUENCE OF CULTIVATION 35 

at the expense of the subsoil water. ^^ Unless rolled 
land receives surface cultivation excessive losses b}- 
evaporation, due to improved capillarity, may result. 
The use of the roller on clay land during a wet season 
results unfavorably. In many localities rolling and 
subsequent surface cultivation are not admissible on 
account of the drifting of the soil, caused by heavy 
winds. 

29. Subsoiling. — By subsoiling is meant pulveri- 
zing the soil immediately under the furrow slice. 
This is accomplished with the subsoil plow, which 
simply loosens the soil without bringing the subsoil to 
the surface. The object of subsoiling is to enable the 
land to retain, near the surface, more of the rainfall. 
Heavy clay lands are sometimes improved by occasional 
subsoiling, but its continued practice is not desirable. 
For orcharding and fruit-growing, it is frequently re- 
sorted to, but is not beneficial on soils containing 
large amounts of sand and silt. Rolling and subsoil- 
ing are directly opposite in effect. Soils which are 
improved by rolling are not improved by subsoiling. 
The additional expense involved should be considered 
when subsoiling is to be resorted to. Experiments 
have not as yet been sufficiently decisive to indicate 
the conditions most favorable for this practice. 

30. Fall Plowing conserves the soil water, by check- 
ing evaporation and leaving the land in better condi- 
tion to retain moisture. Fall plowing should be fol- 



36 SOILS AND FERTILIZERS 

lowed by surface cultivation. Evaporation may take 
place from unplowed land during the fall, and in the 
spring the soil contains appreciably less water than 
plowed land. By fall plowing it is possible to carry 
over a water balance in the soil from one year to the 
next. 

31. Spring Plowing. — When land is plowed late in 
the spring there has been a previous loss of water by 
evaporation, and the soil has not been able to store up 
as much of the rain and snow as if fall plowing had 
been practiced. ^+ Dry soil is plowed under and moist 
soil brought to the surface. This moisture is readily 
lost by evaporation if surface cultivation is not em- 
ployed; good capillary connection of the surface soil 
and subsoil is not obtained, and the furrow slice soon 
becomes dry. 

Surface cultivation should immediately follow both 
spring and fall plowing. 

Per cent, of water in^3 
Fall plowed Spring plowed 

April 25 land. land. 

From 2 to 6 inches 24.7 22.4 

" 6 to 12 " 26.6 24.1 

" 12 to 18 '• 28.8 26.5 

Average difference 2.37 per cent. 

32. Mulching. — The use of well-rotted manure or 
straw, spread over the surface as a mulch, prevents 
evaporation. In forests the leaves form a mulch 
which is an important factor in maintaining the water 
supply. In order that a mulch be effectual, it must 



INFLUENCE OF CULTIVATION 37 

be compacted, — a loose pile of straw is not a mulch. 
In reclaiming lands gnllied by water, mulching is 
very beneficial. A slight mulch may also be used to 
encourage the growth of grass on a refractory hillside. 
When land is mulched, evaporation is checked. Sur- 
face cultivation and mulching may be combined and 
excellent results obtained. '3 

Per cent, of water in 
Mulched straw- 
berry patch. Unmulched. 

Soil 2 to 5 inches 18.12 11. 17 

" 6 to 12 " 22.18 18.14 

" 12 to 18 " 24.31 21. II 

33. Depth of Plowing. — The depth to which a soil 
should be plowed in order to give the best results must, 
of necessity, vary with the conditions. Deep plowing 
of sandy land is not advisable, particularly in the 
spring. On clay land deeper plowing should be the 
rule. The longer a soil is cultivated the deeper and 
more thorough should be the cultivation. While 
shallow plowing is admissible on new prairie land, 
deeper cultivation should be practiced when the land 
has been cropped for a series of years. The depth of 
plowing should be regulated by the season. In the 
prairie regions, and in the northwestern part of the 
United States, shallow plowing is more generally prac- 
ticed than in the eastern states. Deep plowing in the 
fall gives better results than in the spring. It is not 
a wise plan to plow to the same depth every year. 
Prof. Roberts says:'^ "If plowing is continued at one 



38 SOILS AND FERTILIZERS 

depth for several seasons, the pressure of the imple- 
ment and the trampling of the horses in time solidify 
the bottom of the furrow, but if the plowing is shallow 
in the spring and deep in summer and fall, the objec- 
tional hard pan will be largely prevented." 

In regions of scant rainfall deep plowing of silt soils 
should be done only at intervals of three or five years. 
With an average rainfall, deep plowing should be the 
rule on soils of close texture. The depth of plowing 
should be varied to meet the requirements of the crop, 
of the soil and the amount of rainfall. 

34. Permeability of Soils. — The rapidity with 
which water sinks into the soil after a rain depends 
upon the nature of the soil, and upon the cultivation 
which it has received. Shallow surface cultivation 
leaves the soil in good condition to absorb water. 
When the surface is hard and dry a large per cent, of 
the water which falls on rolling land is lost by sur- 
face drainage. Soils of close texture which contain 
but few non-capillary spaces, offer the greatest resist- 
ance to the downward movement of water. 

The term permeable is applied to a soil when it is 
of such a texture that it does not allow the water to 
accumulate and clog the non-capillary spaces. Culti- 
vation may change the texture of even a clay soil to 
such an extent as to render it permeable. Deep 
plowing increases permeability. In regions of heavy 
rains increased permeability is very desirable for good 



INFLUENCE OF CULTIVATION 39 

crop production on heavy clays. Sandy and loamy 
soils have a high degree of permeability, and it is not 
necessary that it should be increased. 

35. Fertilizers. — When water contains dissolved 
salts, it is more susceptible to the influence of surface- 
tension, and is more readily brought to the surface of 
the soil. In commercial fertilizers soluble salts are 
present. The beneficial effects of commercial fertili- 




Fig. 15. Sandy soil without manure. 

zers upon the moisture content of soils are liable to 
be overestimated, because the fertilizer undergoes fix- 
ation when applied, and does not remain in a soluble 
condition. Fertilizers containing soluble salts exercise 
a favorable influence upon the moisture content of 
soils, but the extent of this influence has never been 
determined under field conditions. 

36. Farm Manures. — Well-prepared farm manures 
exercise a beneficial effect upon the moisture content of 
soils. When well-rotted manure is worked into a soil, 
the coarse soil particles and masses are bound together. 



40 



SOILS AND FERTILIZERS 



and the non-capillary spaces are made capillary. The 
free circulation of the air which increases evaporation, 
is prevented when a sandy soil is manured. When 




Fig. 1 6, Sandy soil with manure, 

silt and sandy soils are manured they are capable of 
retaining more water, as shown by the following ex- 
ample :^3 



Fine sandy 

soil. 

Per cent. 



Capacity for holding water 25 



95 per cent, fine 

sandy soil. 

5 per cent. 

dry manure. 

Per cent. 

42 



The manure enables the soil to retain more water 
near the surface and prevents losses by percolation. 
The difference in moisture content of manured and un- 
manured land is particularly noticeable in a dry season. ^3 



Sandy soil 

well manured. 

Water. 

Per cent. 



Sandy soil 

uumanured. 

Water. 

Per cent. 



Soil one to six inches 10.50 

Coarse leached manure may have just 

effect by producing an open and porous condition of 

the soil. 



8.10 
the opposite 



INFI^UENCE OF CULTIVATION 4 1 

37. Drainage. — Good drainage is very essential in 
order to properly regulate the water supply. If the 
water which falls on the land is allowed to flow over 
the surface and is not retained in the soil, there is not 
sufficient reserve water for crop growth. The object 
of good drainage is to store up as much water as pos- 
sible in the subsoil and to prevent surface accumula- 
tion and losses. Good drainage is accomplished by 
thorough cultivation, and in regions of heavy rainfall 
by tile drainage. Well-drained land is warmer in the 
spring, has a larger reserv^e store of water, and is in 
better condition for crop growth. 

38. Influence of Forest Regions. — The deforesting 
of large areas near the source of rivers has an injurious 
influence upon the moisture content of adjoining farm 
lands. By cutting over and leaving barren large tracts, 
less water is retained in the soil. Near forest rep^ions 
the air has a higher moisture content, due to the 
water given off by evaporation. Farm lands adjacent 
to deforested districts lose water more rapidly by 
evaporation, because the air is so much drier. In 
Section 24 it was stated that losses of water by trans- 
piration could be indirectly influenced. This can be 
accomplished by retaining our forest lands. 

Good drainage in agriculture means not only good 
drainage for individual farms, but also good storage 
capacity in the form of forest lands, for the surplus 
water which accumulates near the sources of large 
rivers. 



RELATION OF THE SOIL TO HEAT 

39. The Sources of Heat in soils are (i) solar 
heat, and (2) heat resulting from chemical action. 
Solar heat is the main source for crop produc- 
tion. The action of heat upon soils has been 
studied extensively by Schiibler. The amount of heat 
a soil is capable of absorbing depends upon its texture 
and moisture content. All dark-colored soils have a 
greater power for absorbing heat than light-colored 
ones. From Schiibler's experiments it appears that 
when dry, there may be as great a difference as 8° C, 
between light- and dark-colored soils. When one set 
of soils was covered with a thin white coat of mag- 
nesia, and another set with lampblack, and exposed 
under like conditions, the temperatures were:^ 

White coating^. Black coating. 

Sand 43 50 

Gypsum 43 51 

Humus 42 49 

Clay 41 48 

Loam 42 50 

The presence of water in the soil modifies the power 
for absorbing heat. A sandy soil for example retains 
about 12 percent, of water, while a humus soil retains 
35 per cent. The additional amount of water in the 
humus soil may cause the soil temperature to be lower 
than that of the sandy soil. While the humus soil 
absorbs more heat than the sandy soil, the heat is used 



RELATION OF THE SOIL TO HEAT 43 

up in evaporating water. A sandy soil readily warms 
up in the spring on account of the relatively small 
amount of w^ater which it contains. 

The specific heat of a soil is the amount of heat re- 
quired to raise a given weight i° C, as compared with 
the heat required to raise the same weight of water i °. 
The specific heat of soils ranges from 0.2 to 0.4. 

The effect of drainage upon soil temperature is 
marked. The surface of well-drained land is usually 
several degrees warmer than that of poorly drained 
land. Water being a poor conductor of heat it follows 
that soils which are saturated are slow to warm up in 
the spring. At a depth of 2 or 3 feet there is not such 
amarkeddifferencein the temperature of wet and dry 
soils. It is to be observed that with proper systems of 
drainage the surplus water is removed from the sur- 
face soil and stored up in the subsoil for the future use 
of the crop, and at the same time the temperature of the 
surface soil is raised, thus improving the conditions for 
crop growth. The relation of drainage to the proper 
supply of water and temperature for crop growth is a 
matter which generally receives too little consideration 
in field practice. 

40. Heat from Chemical Reactions within the 
Soil. — Heat also results from the slow oxidation of 
the organic matter of the soil. When organic matter 
decomposes, it produces heat. A load of manure, when 
it rots in the soil, gives off the same amount of heat as 



44 SOILS AND FERTILIZERS 

if it were burned. Manured land is usually i° or 2° 
warmer in the spring than unmanured land ; this is due to 
the oxidation of the manure. In an acre of rich prairie 
soil it has been estimated that the amount of organic 
matter which undergoes oxidation produces as much 
heat annually as would be produced from a ton of 
coal.^^ In well-drained and well-manured land, the 
additional heat is an important factor for stimulating 
crop growth, particularly in a cold, backward spring. 
The production of heat from manure is illustrated in 
the case of hotbeds where well-rotted manure is covered 
with soil ; this results in raising the temperature of the 
soil. When soils are well manured, heat is retained 
more effectually. In the case of early frosts, crops on 
well-manured land will often escape. 

41. Relation of Heat to Crop Growth. — All plant 
life is directly dependent upon solar heat as the source 
of energy for the production of plant tissue. The 
heat of the sun is the main force at the plant's dis- 
posal for decomposing water and carbon dioxide and 
for producing starch, cellulose, and other compounds. 
The growth of crops is the result of the transformation 
of solar heat into chemical energy which is stored up 
in the plant. When the plant is used for fuel or for 
food the quantity of heat produced by complete oxida- 
tion is equal to the amount of heat required for forma- 
tion. 



COLOR OF SOILS 

42. Organic Matter and Iron Compounds. — The 

principal materials which impart color to soils are or- 
ganic matter and iron compounds. Soils containing 
large amounts of organic matter are dark-colored. 
A union of the decaying organic matter and the 
mineral matter of the soil also produces compounds, 
brown or black in color. When moist, many soils are 
darker than when dry, and soils in which the organic 
matter has been kept up by the use of manures are 
darker than unmanured soils.'^ When rich, black, 
prairie soils lose their organic matter through im- 
proper methods of cultivation or when the organic 
matter (humus) is extracted in chemical analysis the 
soils become light-colored. 

The red color of soils is imparted by ferric oxide, 
the yellow by smaller amounts of the same material. 
The greenish tinge is supposed to be due to the pres- 
ence of ferrous compounds, such soils being so close in 
texture as to exclude the oxidizing action of the air. 
Black and yellow soils are, as a rule, the most produc- 
tive. Color may serv^e, to a slight extent, as an index 
of fertility. The main reason why black soils are so 
generally fertile is because they contain a higher per 
cent, of nitrogen. Black soils are occasionally unpro- 
ductive because of the presence of compounds injurious 
to vegetation. 



46 SOILS AND FERTILIZERS 

43. Odor and Taste of Soils. — Soils containing 
liberal amounts of organic matter have character- 
istic odors. The odoriferous properties of a soil are 
due to the presence of aromatic bodies produced by 
the decomposition of organic matter. In cultivated 
soils these bodies have a neutral reaction. Poorly 
drained peaty soils give off volatile acid compounds 
when dried. The amount of aromatic compounds in 
soils is very small. 

The taste of soils varies with the chemical compo- 
sition. Poorly drained peaty soils usually have a 
slightly sour taste, due to the presence of organic 
acids. Alkaline soils have variable tastes according 
to the prevailing alkaline compound. The taste of 
a soil frequently reveals a fault, as acidity or alka- 
limetry. 

44. Power of Soils to Absorb Gases. — All soils pos- 
sess, to a variable extent, the physical power of absorb- 
ing gases. When decomposing animal or vegetable 
matter is mixed with the soil the gaseous products 
given off are absorbed. The absorption is both a 
chemical and a physical action. The chemical 
changes which occur, as the absorption of ammonia, 
are considered in the chapter on fixation. The organic 
matter of the soil is the principal agent in the physical 
absorption of gases; peat, for example, has the power 
of absorbing large amounts. This action is similar 
to that of a charcoal filter in removing noxious 
gases from water. 



COLOR OF SOILS 47 

45. Relation of Soils to Electricity. — There is 
always a certain amount of electricity in both the soil 
and the air. The part which it takes in plant growth 
is not well understood. The action of a strong cur- 
rent upon the soil undoubtedly results in a change in 
chemical composition ; a feeble current has either an 
indifferent or a slightly beneficial effect upon crop 
growth. In order to change the composition of the 
soil so as to render the unavailable plant food available, 
would require a current destructive to vegetation. 
When plants are subjected to too strong a current of 
electricity, they wilt and have all of the after-appear- 
ance of frost. The slightly beneficial action upon 
plant growth is not sufficient to warrant its use as yet 
in general crop production on account of cost. The 
action of a weak current of electricity upon plants is 
undoubtedly physiological rather than chemical, unless 
it be in the slightly favorable influence which it exerts 
upon nitrification. The resistance which soils, when 
wet, offer to electricity has been taken by Whitney as 
the basis for the determination of moisture in soils. '^ 

46. Importance of the Physical Study of Soils. — 
From what has been said regarding the physical prop- 
erties of soils it is evident that such a study will give 
much valuable information regarding their probable 
agricultural value. While the physical properties 
should always be taken into consideration, they should 
not form the sole basis for judging the character of a 



48 SOILS AND FERTILIZERS 

soil, because two soils from the same locality frequently 
have the same general physical composition and still 
have entirely different crop-producing powers, due to 
a difference in chemical composition. 

Attempts have been made to overestimate the value 
of the physical properties of soils and to explain nearly 
all soil phenomena on the basis of soil physics. Im- 
portant as are the physical properties of a soil, it can- 
not be said that they are or more importance than the 
chemical properties. In fact the four sciences, chem- 
istry, physics, geology, and bacteriology, are all closely 
connected and each contributes its part to our knowl- 
edge of soils. 



CHAPTER II 

GEOLOGICAL FORMATION AND CLASSIFICATION OF SOILS 

47. Geological Study of Soils. — The geological 
study of a soil concerns itself with the past history of 
that soil, the material out of which it has been pro- 
duced, together with the agencies which have taken a 
part in its formation and distribution. Geologically, 
soils are classified according to the period in the earth's 
history when formed, and also according to the agen- 
cies which have distributed them. Agricultural geology 
is of itself a separate branch of agricultural science. 
The principles of soil formation and soil distribution 
should be understood, because they have such an im- 
portant bearing upon soil fertility. In this work, only 
a few of the more important topics of agricultural 
geology are treated in a general way. 

48. Formation of Soils. — Many geologists believe 
the surface of the earth to have been at one time solid 
rock. It is now almost universally held that soils 
have been formed from rock by various agents ; as, ( i ) 
heat and cold, (2) water, (3) gases, (4) micro-organisms 
and vegetable life. The disintegration of rock is 
usually effected by the combined action of these vari- 
ous agents. The process of soil formation is a slow 
one and the various agents have been at work for an 
almost indefinite period. 



50 SOILS AND FERTILIZERS 

49. Action of Heat and Cold. — The cooling of the 
earth's surface, followed by a contraction in volume, 
resulted in the formation of fissures which exposed a 
larger area to the action of other agents. The unequal 
cooling of the rock caused a partial separation of the 
different minerals, resulting in the formation of smaller 
rock particles from larger rock masses. This is well 
illustrated by the familiar splitting and crumbling of 
many stones when heated. The action of frost upon 
rock is also favorable to soil formation. The freezing 
of water in rock crevices results in breaking up the 
rock masses, forming smaller bodies. The force ex- 
erted by water when it freezes is sufiicient to detach 
large rocks. 

50. Action of Water. — Water acts upon soils both 
chemically and physically. In its physical action, 
water has been the most important agent that has 
taken a part in soil formation. The surface of rocks has 
been worn away by moving water and in many cases deep 
ravines and canons have been formed ; the pulverized 
rock, being carried along by the water and deposited 
under favorable conditions, forms alluvial soil. This 
is illustrated in the workings of large rivers where the 
pulverized rock masses are deposited along the river 
and at its mouth. A large portion of the soil in 
valleys and river bottoms has been deposited by water. 
The action of water is not alone confined to the forma- 
tion of soils along water courses, but is equally impor- 



CLASSIFICATION OF SOILS 5 1 

tant in the formation of soils remote from streams or 
lakes, as in the case of soils deposited by glaciers. 

51. Glacial Action. — At one time in the earth's 
history, the ice-fields of polar regions covered much 
larger areas than at present. ^9 Changes of climate 
caused a recession of the ice-fields, and resulted in the 
movement of large bodies of ice, carrying along rocks 
and frozen soil. The movement and pressure of the 
ice pulverized the rock and produced soil. This 
action is well illustrated at the present time where 
mountains rise above the snow line, and the ice and 
snow melting at the base are replaced by ice and 
snow from above moving down the side of the moun- 
tain. When the glacier receded, stranded ice masses 
were distributed over the land. These melted slowly 
and by their grinding action hollowed out places 
which finally became lakes. The numerous lakes at 
the source of the Mississippi River and in central Min- 
nesota are supposed to have been formed by glacial 
action. The terminal of a glacier is called a moraine 
and is covered with large boulders which have not 
been disintegrated. The course of a glacier is fre- 
quent!}' traced by the markings or scratches of the 
mass on rock ledges. In glacial soils, the rocks are 
never angular, but are smooth because of the grinding 
action during transportation. The area of glacial soils 
in the northern portion of the United States is quite 
large. These soils are, as a rule, fertile because of 



52 SOILS AND FERTILIZERS 

the pulverization and mixing of a great variety of 
rock. 

52. Chemical Action of Water. — The chemical 
action of water has not taken such an important 
part in soil formation as the physical action. While 
nearly all recks are practically insoluble in water 
there is always some material dissolved, evidenced by 
the fact that all spring-water contains dissolved 
mineral matter. When charged with carbon dioxide 
and other gases, water acts as a solvent upon rocks. 
It converts many oxides, as ferrous oxide, into hy- 
droxides. The chemical action of water may result in 
the formation of new compounds more soluble or 
readily disintegrated, as deposits of clay, which have 
been produced by the chemical and physical action of 
water upon feldspar rock. Limestone is quite readily 
disintegrated by water, which produces many chemical 
changes in both rocks and soils. The chemical action 
of fertilizers known as fixation can take place only in 
the presence of water. In fact water is necessary for 
nearly all chemical reactions in the soil. 

53. Action of Air and Gases. — The part which air 
has taken in soil formation has not been as prominent 
as that taken by water. By the aid of oxygen, carbon 
dioxide, and other gases and vapors in the air, rock 
disintegration is hastened. The action of oxygen 
changes the lower oxides to higher forms. All rock 
contains more or less oxygen in chemical combination. 



CLASSIFICATION OF SOILS 53 

The carbon dioxide of the air under some conditions 
favors the formation of carbonates. The disinte- 
grating action of air, moisture, and frost is illustrated 
in the case of building stones which in time crumble 
and form a powder. The combined action of air, 
moisture, and frost is called weathering. 

54. Action of Vegetation. — Some of the lower 
forms of plants as lichens do not require soil for 
growth, but are capable of living on the bare surface 
of rocks, obtaining food from the air, and leaving a 
certain amount of vegetable matter which under- 
goes decay and is incorporated with the rock parti- 
cles, preparing the way for higher orders of plants 
which take their food from the soil. When this 
vegetable matter decays it enters into chemical com- 
bination with the pulverized rock, forming humates.^^ 
The disintegrating action of plant roots and vegetable 
matter upon rocks has been an important factor in 
soil formation. 

55. Action of Micro-organisms. — Micro-organisms, 
found on the surface and in the crevices of rocks, are 
considered by many as active agents in bringing about 
rock decay. The nitrifying organisms have taken 
an important part in rendering soils fertile, and these 
with others have without doubt aided in soil forma- 
tion. Some of the organisms found on the surface of 
rocks are capable of producing carbonaceous matter 
out of the carbon dioxide and other compounds of 



54 SOILS AND FERTILIZERS 

the air.^° This action results in adding vegetable 
matter to the soil. 

56. Combined Action of the Various Agents. — In 

the decay of rocks the various agents named, — water 
acting mechanically and chemically, heat and cold, 
air, and vegetation, — have been acting jointly, and have 
produced a more rapid disintegration than if each 
agent were acting separately. One of the best evi- 
dences that soil is derived from rock is that there are 
frequently found in fields pieces of rock which are 
actually rotten, and, when crushed, closely resemble 
the prevailing soil of the field. This is particularly 
true of clay soils where fragments of disintegrated 
feldspar are found which, when crushed, resemble the 
soil in which the feldspar was imbedded. 

DISTRIBUTION OF SOILS 

57. Sedentary and Transported Soils. — The place 
where a soil is found is not necessarily the place where 
it was produced ; that is, a soil may be produced in 
one locality and transported to another. Soils are 
either sedentary or transported. Sedentary soils are 
those which occupy the original position where they 
were formed. They usually have but little depth be- 
fore rock surface is reached. The stones in such soils 
have sharp angles because they have not been ground 
by transportation. Transported soils are those 
which have been formed in one locality and carried by 



ROCKS AND MINERALS 55 

various agents as glaciers and rivers, to other locali- 
ties, the angles of stones in these soils being ground off 
during transportation. Transported soils are divided 
into classes according to the ways in which they have 
been formed ; as, drift soils produced by glaciers, and 
alluvial soils formed by rivers and deposited by lakes. 
Other agents which have taken a part in soil 
transportation are wind and volcanic action. Many 
soils have been either formed or modified by the wind. 
The denuding action of heavy wind storms upon many 
prairie soils is well known. Soil particles are carried 
long distances and then deposited, forming wind-drifted 
soils. In some localities volcanic soils are found ; they 
are extremely varied in texture and composition — some 
are very fertile and contain liberal amounts of alka- 
line salts and phosphates, while others contain so little 
plant food that they are sterile. 

ROCKS AND MINERALS FROM WHICH SOILS ARE FORMED 

58. Composition of Rock. — Rocks are composed of 
either a single mineral or of a combination of minerals. 
Most of the common minerals have a variable rangre of 
composition, due to the fact that one element or com- 
pound may be partially or entirely replaced by another. 
Most of the common rocks from which soils have been 
produced are composed of feldspar, mica, hornblende, 
and quartz. 

59. Quartz and Feldspar. — Quartz is the principal 

constituent of many rock formations. Pure quartz is 



56 SOIIvS AND FERTII^IZERS 

silicic anhydride (SiOJ. White sand is nearly pure 
quartz. A soil formed from pure quartz would be 
sterile. Feldspar is composed of silica, alumina, and 
potash or soda. Lime may also be present, and re- 
place a part or nearly all of the soda. If the mineral 
contains soda as the alkaline constituent it is known 
as albite, or if mainly potash it is called potash feld- 
spar or orthoclase. 

The members of the feldspar group are insoluble in 
acids and before disintegration takes place are not ca- 
pable of supplying plant food. Potash feldspar contains 
from 12 to 15 per cent, of potash, none of which is of 
value as plant food. When feldspar undergoes disin- 
tegration it produces clay. A soil formed from feld- 
spar is usually well stocked with potash. 

Orthoclase, AlKSii^Oy Potash Feldspar. 

Albite, AlNaSiyOg Sodium Feldspar. 

60. Hornblende. — The hornblende and augite groups 
are formed by the union of magnesium, calcium, iron, 
and manganese, with silica. There are none of the 
members of the alkali family in hornblende. The au- 
gites are double silicates of iron, manganese, calcium, 
and magnesium. Quite frequently phosphoric acid is 
present in chemical combination with the iron. The 
members of this group are readily distinguished by 
their color which is black, brown, or brownish green. 
The hornblendes are insoluble in acids, hence unavail- 



ROCKS AND MINERALS 57 

able as plant food, and when disintegrated do not as a 
rule form very fertile soils. 

6i. Mica. — Mica is quite complex in composi- 
tion, is an abundant mineral, and is composed of sil- 
ica, iron, alumina, manganese, calcium, magnesium, 
and potassium. Mica is a polysilicate. The color 
may be white, brown, black, or bluish green owing 
to the absence of iron, or to its presence in various 
amounts. The chief physical characteristic of the 
members of this group is the ease with which they 
are split into thin layers. It is to be observed that the 
mica group contains all of the elements of both feld- 
spar and hornblende. 

Soils formed from the disintegration of mica are 
usually fertile owing to the variety of essential ele- 
ments present. Frequentlv small pieces of undecom- 
posed mica are found in soils. 

62. Zeolites. — The zeolites form a large group of 
secondary minerals. They are polysilicates containing 
alumina and members of the alkali and lime fami- 
lies, and all contain water held in chemical combina- 
tion. They are soluble in dilute hydrochloric acid 
and belong to the group of compounds which are ca- 
pable, to a certain extent, of serving as plant food. In 
color they are white, gray, or red. Zeolites are quite 
abundant in clay and are an important factor in soil 
fertility. It is this group which takes such an impor- 
tant part in the process of fixation. The zeolites, when 



58 SOILS AND FERTILIZERS 

disintegrated, particularly by glacial action, form very 
fertile soils. 

63. Granite is composed of quartz, feldspar, and 
mica. It is a very hard rock and is slow to disinte- 
grate. The different shades of granite depend upon 
the proportion in which the various minerals are pres- 
ent. Inasmuch as granite contains so many minerals 
it usually follows that thoroughly disintegrated granite 
soil is very fertile. Pure powdered granite before un- 
dergoing disintegration furnishes no plant food. After 
weathering, the plant food gradually becomes availa- 
ble. Gneiss belongs to the granite series but differs 
from true granite by containing a larger amount of 
mica. Mica schist contains a larger amount of mica 
than gneiss. 

64. Apatite or Phosphate Rock. — Apatite is com- 
posed mainly of phosphate of lime, Ca (PO )^, together 
with small amounts of other compounds as fluorides 
and chlorides. This mineral is generall}' of a green 
or yellow color. It is present in many soils and is 
of little value as plant food unless associated with or- 
ganic matter or some soluble salts. 

65. Kaolin is chemically pure clay and is formed by 
the disintegration of feldspar. When feldspar is de- 
composed and is acted upon by water the potash is re- 
moved and water of hydration is taken up, forming 
the product kaolin, which is hydrated silicate of alu- 
mina, Al (SiO ) .H^O. Impure varieties of clay are col- 



ROCKS AND MINERALS 59 

ored red and yellow on account of the presence of iron 
and other impurities. Pure kaolin is white, is in- 
soluble in acids, and is incapable of supplying any 
nourishment to plants. Clay soils are fertile on ac- 
count of the other minerals and organic matter mixed 
with the clay and are usually well stocked with pot- 
ash because of the incomplete removal of the potash 
from the disintegrated feldspar. It is to be observed 
that the term clay used chemically means alu- 
minum silicate, while physically it is any substance, the 
particles of which are less than 0.005 mm. in diameter. 
66. Other Rocks and Minerals. — In addition to 
the rocks and minerals which have been discussed, 
there are many others that contribute to soil forma- 
tion, as limestone, which is calcium carbonate ; dolo- 
mite, a double carbonate of calcium and magnesium ; 
serpentine, a silicate of magnesium ; and gypsum, cal- 
cium sulphate. 

Chemical Composition of Rocks '" 



In" ti lo 4°^ EO ^a 'EO ^6 

■^•^ <^^ cl^ ^Z h40 SS ^^ ^M 

Quartz 95-100 

Feldspar 55-67 20-29 0-12 i-io i-ii 

Kaolin 46 ^9 ^4 

/p o \ 
Apatite - 53 •••• WaV •••' 

Mica 40-45 12-37 5-12 1-5 

Hornblende.. 40-55 0-15 

Granite 60-80 10-15 4-5 2-3 • • • 



CHAPTER III 

THE CHEMICAL COMPOSITION OF SOILS 

67. Elements Present in Soils. — Physically consid- 
ered, a soil is composed of disintegrated rock mixed 
with animal and vegetable matter ; chemically consid- 
ered, the rock particles are composed of a large 
number of simple and complex compounds, each 
compound in turn being composed of elements chem- 
ically united. Elements unite to form compounds, 
compounds to form minerals, minerals to form rocks, 
and disintegrated rocks form soil. When rocks decom- 
pose, the disintegration, except in a few cases, is never 
carried to the extent of liberating the elements, but 
the process ceases when the minerals have been broken 
up into compounds. While there are present in the 
crust of the earth between 65 and 70 elements, only 
about 15 are found in animal and plant bodies, and of 
these but 12 are absolutely essential. Only four of 
the elements which are of most importance are at all 
liable to be deficient in soils. These four elements 
are : nitrogen, phosphorus, potassium, and calcium. 

68. Classification of the Elements. — The elements 
found most abundantly in soils are divided into two 
classes : 



CHEMICAL COMPOSITION OF SOILS 6 1 

Acid-forming elements Base-forming- elements 

Oxygen O Aluminum Al 

Silicon Si Potassium K 

Phosphorus P Sodium Na 

Sulphur S Calcium Ca 

Chlorine CI Magnesium Mg 

Nitrogen N Iron Fe 

Hydrogen H 

Boron, fluorine, manganese, and barium are usually 
present in small amounts, besides others which may 
be present in traces, as the rare elements lithium and 
titanium. 

For crop purposes the elements of the soil may be 
divided into three classes : 

1. Essential elements most liable to be deficient : 
nitrogen, potassium, phosphorus, and calcium. 

2. Essential elements usually abundant : iron, mag-- 
nesium, and sulphur. 

3. Unnecessary and accidental elements, usually 
abundant, as chlorine, silicon, aluminum, and man- 
ganese. 

69. Combination of Elements. — In dealing with 
the composition of soils the percentage amounts of the 
individual elements are not given, except in the case 
of nitrogen ; but instead, the percentage amounts of 
the various oxides. This is because the elements do 
not exist as free elements in the soil, but are combined 
with oxygen and other elements to form compounds. 
When considered as oxides the acid- and base-forming 
elements may form various compounds as : 




62 SOILS AND FERTILIZERS 

f Silicate 
I Phosphate 

Calcium -j Chloride 

Sulphate 
Carbonate 
Potassium 
Sodium . . 
Magnesium - 
Iron 

The following reactions will explain some of the 
more elementary forms of combinations : 

CaO + SiO, =: CaSiO, CaO + SO, = CaSO, 

SCaO + PA =Ca3(P0,), K,0 + SO* =. K,SO, 

CaO + SO3 = CaSO, Na,0 + SO, = Na,SO, 

CaO + CO2 = CaCO.; MgO + SO, = MgSO^ 

When considered as the oxide, calcium may com- 
bine with any of the oxides of the acid-forming ele- 
ments, as indicated by the reactions, to form salts. 
Each of the compounds formed from the more 
common elements may have a separate value as plant 
food, hence it is important to consider the combina- 
tions of each element separately. 

ACID-FORMING ELEMENTS 

70. Silicon. — The element silicon makes up from 
a quarter to a third of the solid crust of the earth and 
next to oxygen is the most abundant element found 
in the soil. Silicon never occurs in the soil in the 
free state. It either combines with oxygen to form 
silica (SiOJ, or with oxygen and some base-forming 
element or elements to form silicates. Silica and the 
various silicates are by far the most abundant com- 



ACID-FORMING ELEMENTS 6 



v) 



pounds present in the soil. Silicon is not one of the 
elements absolutely necessary for plant growth, and 
even if it were, all soils are so abundantly supplied 
that it would not be necessary to use it in fertilizers. 

71. Double Silicates. — When tw^o or more base- 
forming elements are united with the silicate radical, 
a double silicate is formed. In fact the double sili- 
cates are the most common forms present in soils. 
There are also a number of forms of silicic acid which 
o:reatlv increase the number of silicates, and a study of 
the composition of soils is largely a study of these 
various silicates. 

72. Carbon is an acid-forming element and belongs 
to the same family as silicon ; it is found in the soil 
as one of the main constituents of the volatile or 
organic compounds. Carbon also unites with oxygen 
and the base-forming elements, producing carbonates, 
as calcium carbonate or limestone. The carbon of the 
soil takes no direct part in forming the carbon com- 
pounds of the plant. It is not necessary to apply 
carbon fertilizers to produce the carbon compounds of 
plants because the carbon dioxide of the air is the 
source for crop production. It is estimated that there 
are 30 tons of carbon dioxide in the air over every 
acre of the earth's surface.^' The carbon in the soil is 
an indirect element of fertility, because it is usually 
combined with elements, as nitrogen and phosphorus, 
which are absolutely necessary for crop growth. 



64 SOILS AND FERTILIZERS 

73. Sulphur occurs in all soils mainly m the form 
of sulphates, as calcium sulphate, magnesium sul- 
phate, and sodium sulphate. It is an important ele- 
ment of plant food. There is generally less than one- 
half percent, of sulphuric anhydride in ordinary soils, 
but the amount required by crops is small and there 
is usually an abundance in all soils. 

74. Chlorine is present in all soils, generally in 
combination with sodium, as sodium chloride. It may 
be in combination with other bases. Soils which con- 
tain more than o. 10 per cent, are, as a rule, sterile. Chlo- 
rine is present in the soil in soluble forms. It occurs in 
all plants, although it is not absolutely necessary for 
plant growth, hence its combination in fertilizers is 
unnecessary. Chlorine with sodium, as common salt, 
is sometimes used as an indirect fertilizer. 

75' Phosphorus, one of the essential elements for 
plant growth, is combined with both the volatile and 
non-volatile elements of the soil. Plants cannot make 
use of it in other forms than those of phosphates. 
Phosphorus is usually present in the soil as calcium 
phosphate, magnesium phosphate, or aluminum phos- 
phate, and may also be combined with the humus, 
forming humic phosphates. The form in which the 
phosphates are present, as available or unavailable, is 
an important factor in soil fertility. Soils are quite 
liable to be deficient in phosphates, inasmuch as they 
are so largely drawn upon by many crops, particularly 



ACID-FORMING ELEMENTS 65 

grain crops where the phosphates accumulate in the 
seed, and are sold from the farm. 

76. Nitrogen. — This element is present in soils in 
various forms. As a mineral constituent it is combined 
with oxygen and the base-forming elements as potassium, 
sodium, or calcium, forming nitrates and nitrites, which, 
on account of their solubility, are never found in ordi- 
nary soils in large amounts. Nitrogen is present 
mainly in organic combinations, being associated with 
carbon, hydrogen, and oxygen as one of the elements 
forming the organic matter of soils. Nitrogen may 
also be present in small amounts in the form of am- 
monia, or of ammonium salts, derived from rain 
water and from the decay of vegetable and animal 
matter. While nitrogen is present in the air, in a free 
state, in large amounts, it can be appropriated indirectly 
as food in this form by only a limited number of plants. 
For ordinary agricultural crops, particularly the cere- 
als, nitrogen must be supplied through the soil as com- 
bined nitrogen. This element is the most expensive 
and is liable to be the most deficient of any of the ele- 
ments of plant food. No other element takes such an 
important part in agriculture or in life processes. 

77. Oxygen. — Oxygen is combined w4th both the 
acid- and base-forming elements and is present in 
nearly all of the compounds of the soil. It has been 
estimated that about one-half of the crust of the earth 
is composed of oxygen, which is found in large pro- 



66 SOILS AND FERTILIZERS 

portions combined with silicon, forming silica. That 
which is held in chemical combination in the soil 
takes no part in the formation of plant tissue. In ad- 
dition to being present in the soil, oxygen constitutes 
eight-ninths of the weight of water and about one-fifth 
of the weight of air. It also forms about 50 per cent, 
of the compounds found in plants and animals. Oxy- 
gen in the interstices of the soil is an active agent in 
bringing about many chemical changes, as oxidation 
of the organic matter, and disintegration of the soil 
particles. 

78. Hydrogen. — This element is never found in a 
free state in the soil, but is combined with carbon and 
oxygen as in animal and vegetable matter, with oxy- 
gen to form water, and in a few cases with some of 
the base elements to form hydroxides. It is not found 
in large amounts in the soil, and that which forms a 
part of the tissues of plants and animals comes from 
the hydrogen in water. Hydrogen in the organic 
matter of soils takes no part directly in producing the 
hydrogen compounds of plants. On account of its 
lightness, hydrogen never makes up a very large pro- 
portion, by weight, of the composition of bodies. 

BASE-FORMING ELEMENTS 

79. Aluminum is present in the soil in the largest 
quantity of any of the base elements. It is calculated 
that from 6 to 10 per cent, of the solid crust of the 
earth is aluminum. As previously stated it is one of 



BASE-FORMING ELEMENTS 67 

the constituents of clay, and furnishes nothing for 
plant growth. Physically, however, the aluminum 
compounds take an important part in soil fertility. 
Aluminum is usually in combination with silica or 
with silica and some base-forming element, as iron, 
potassium, or sodium. The various forms of alumi- 
num silicates are the most numerous compounds 
present in soils. 

80. Potassium is present in the soil mainly in 
the form of silicates, and is one of the elements abso- 
lutely necessary for plant growth. The term potash 
(potassium oxide, K^O) is usually employed when the 
potassium compounds are referred to. The amount 
and form of the soil potash have an important bearing 
upon fertility. Potassium is one of the three elements 
of plant food usually supplied in fertilizers. The 
form in which it is present in the soil and its economic 
supply as plant food, are important factors of crop 
growth, and are considered in detail in Chapter VIII. 
The amount of potash in soils ranges from 0.02 to 0.8 
per cent. In a fertile soil it rarely falls below 0.2 per 
cent. 

81. Calcium is present in the soil in a variety of 
forms, as calcium carbonate, calcium silicate, and 
calcium phosphate. The calcium oxide (CaO) of 
the soil is generally spoken of as the lime content. 
Calcium carbonate and sulphate are important factors 
in imparting fertility. A subsoil with a good supply 



68 SOILS AND FERTILIZERS 

of lime will stand heavy cropping and remain in 
excellent chemical and physical condition for crop 
growth. In a good soil there is usually 0.2 of a per 
cent, or more of lime mainly as calcium carbonate. 

82. Magnesium is present in all soils and is usually 
associated with calcium, forming the mineral dolo- 
mite, which is a double carbonate of calcium and 
magnesium. Magnesium may also be present in the 
soil in the form of magnesium sulphate or magnesium 
chloride. All crops require a certain amount of 
magnesia in some form, in order to reach maturity 
and produce fertile seeds. There is generally in all 
soils an amount sufficient for crop purposes, hence it is 
not necessary to consider this element in connection 
with soil fertility. 

83. Sodium is found in the soil mainly as sodium 
silicate, and is present to about the same extent as 
potassium which it resembles chemically in many ways; 
it cannot, however, replace the element potassium. 
Inasmuch as sodium takes such an indifferent part in 
plant nutrition it is never used as a fertilizer except in 
an indirect way. 

84. Iron is an element necessary for plant food and 
is found in all soils to the extent of from i to 4 per 
cent. Crops require only a small amount of iron, 
hence there is always sufficient for crop purposes. 
Iron is present in soils in the form of oxides, hy- 
droxides, and silicates. 



FORMS OF PLANT FOOD 

85. Three Classes of Compounds. — For agricul- 
tural purposes, compounds present in soils may be 
divided into three classes : ^^ The first class includes 
silicates and other compounds of potash, soda, lime, 
magnesia, phosphorus, etc., which are soluble in the 
soil-water and in dilute organic acids. This class 

23 



\\\\\\\\\\\\Mt^^ 



n 






^/^/ //?Jo/aA/e /V^//er 



Fig. 17. Average composition of soils. 
I. Nitrogen; 2, Potash; 3. Phosphoric acid. 

represents the most soluble and the most active and 
valuable forms of plant food. There is only a very 
small amount in these forms. In 100 pounds of soil, 
rarely more than a few hundredths of a pound of any 
one of the important elements is soluble in the soil- 
water or in dilute organic acids. 



JO SOII.S AND FERTII^IZERS 

The plant food of the second class is in a somewhat 
more insoluble form, and consists of all those com- 
pounds and silicates which are soluble in hydrochloric 
acid of twenty-three per cent, strength, 1.115 sp. gr. 
This class of compounds represents the limit of the 
solvent action of the stronger solutions of organic 
acids, such as are found in the roots of plants. 

The third class of silicates includes all of those com- 
pounds which require the combined action of the 
highest heat and the strongest chemicals and fluxes in 
order to decompose them. 

The first and second classes of silicates and other 
compounds are the only ones which possess any value 
as plant food. The third class, after undergoing the 
combined action of the various disintegrating agencies 
of nature, may be changed into the second class, 
called the zeolitic silicates. In this second class are 
also included all of the mineral elements combined 
with the humus. As a rule, not over fifteen or twenty 
per cent, of the total soil is in forms soluble in hydro- 
chloric acid ; and of the more important elements only 
one to six per cent, form a part of this fifteen. In 
two hundred samples of soil, the potash, nitrogen, 
lime, magnesia, phosphoric and sulphuric acids, 
amounted to 3.5 per cent. (Fig. 17). In many fertile 
soils the sum of the nitrogen, phosphoric acid, potash, 
lime, magnesia, and sulphuric and carbonic anhydrides 
is less than i. 50 per cent. This means that in every 100 



FORMS OF PLANT FOOD 



71 



pounds of soil there are only from 1.5 to 3.5 pounds of 
matter which can take any active part in the support 
of a crop, and 96 to 98.5 pounds are present simply as 
so much inert material. 

86. Acid-insoluble Matter of Soils. — The insoluble 
residue obtained after digest- 
ing a soil with strong hydro- 
chloric acid, contains potash, 
soda, and limited amounts of 
magnesia, and phosphoric 
acid, with other elements 
which are of no value as 
plant food. If a seed were 
planted in soil extracted with 
strong hydrochloric acid, it 
would make no growth after 
the reserve food in the seed 
had been exhausted. A plant 
grown in such a soil is shown 
in the illustration (Fig. 18). 

On the other hand it can- 
not be said that all of the 
plant food soluble in hydro- 
chloric acid is equally valu- 
able. In fact, the acid repre- 
sents more than the limit of 

the crop's feeding power. Fig. 18. Oat plant grown in 
1 , -I • , -u r soil extracted with hydro- 

wnen there is not enough 01 chloric acid. 




72 SOILS AND FERTILIZERS 

more soluble forms to aid in the first stages of growth. 
In the following table the percentage amounts of 
compounds soluble and insoluble in hydrochloric acid 
are given : ^^ 

wheat Heavy clay Grass and 
soil. soil. grain soil. 
Solu- Insolu- Solu- Insolu- Solii- Insolu- 
ble in ble ble ble ble ble 
HCl residue in HCl residue in HCl residue 

Insoluble matter. 63.07 84.77 84.08 

Potash 0.54 2.18 0.21 3.46 0.30 1.45 

Soda 0.45 3.55 0.22 2.95 o.?5 0.25 

Lime 2.44 0.36 0.48 0.16 0.51 0.35 

Magnesia 1.85 0.25 0.34 0.47 0.26 0.46 

Iron 4.18 0.78 3.76 0.72 2.56 1.07 

Alumina 7.89 5.54 6.26 5.44 2.99 9.72 

Phosphoric acid . 0.38 0.12 0.08 0.23 0.05 

Sulphuric acid. . . o.ii 0.24 0.09 0.25 0.08 0.02 

The insoluble matter after digestion with hydro- 
chloric acid, was submitted to fusion analysis, and the 
figures given under insoluble residue represent the 
amounts of potash, soda, etc., insoluble in acids. In 
the clay soil 96 per cent, of the total potash is in forms 
insoluble in hydrochloric acid. 

87. Soluble and Insoluble Potash and Phosphoric 
Acid. — From the preceding table it is to be observed 
that the larger portion of the potash in the soil is in- 
soluble in hydrochloric acid. A soil may contain 
from 2 to 3 per cent, of total potash, and 90 per cent, 
or more may be in such firm chemical combination 
with aluminum, silicon, and other elements, as to re- 
sist the solvent action of plant roots. The larger 



FORMS OF PLANT FOOD 73 

portion of the phosphoric acid of the soil is soluble in 
hydrochloric acid. In some soils, however, from 20 
to 40 per cent, is present in the third class of com- 
pounds. When a soil is digested with hydrochloric 
acid, the insoluble residue is usually a fine gray 
powder. Some clay soils retain their red color even 
after treatment with acids showing that the iron is in 
part in chemical combination with the more complex 
silicates. 

In order to decompose the insoluble residue obtained 
from the treatment with hydrochloric acid, fluxes, as 
sodium carbonate and calcium carbonate, are employed 
which act upon the complex silicates at a high tem- 
perature, and produce silicates soluble in acids. 
Plants, however, are unable to obtain food in such 
complex forms of chemical combination. 

88. How a Soil Analysis is Made. — A sample is 
obtained from a field by taking several small samples 
to a depth of 6 to 9 inches, from different places, and 
uniting them to form one sample. All coarse stones 
and roots are removed and a record is made of the 
amount of these materials. The soil is air dried, the 
hard lumps are crushed, and the materials passed 
through a sieve with holes 0.5 mm. in diameter. Only 
the fine earth is used for the chemical analysis. Ten 
grams of soil are weighed into a soil digestion flask, 
and 10 cc. hydrochloric acid of 1.115 sp.gr. are added 
for every gram of soil used. The digestion flask is 



74 



SOILS AND FERTILIZERS 




provided with a glass stopper which is connected with 
a condensing tnbe. The soil digestion flask is then 
placed in a hot water-bath and the di- 
gestion is carried on for twelve hours at 
the temperature of boiling water. After 
the digestion is completed the contents 
of the flask are transferred to a filter and 
separated into an insoluble part, and the 
acid solution which contains the com- 
pounds of the various elements. The 
following table will give a general idea 
of how the different materials are ob- 
tained from the acid solution. This table 
is not intended as an outline for soil 
analysis, but simply to give the stu- 
dent of general chemistry an idea of how an analysis 
is made. 

The second half of the acid solution is divided into 
three portions. The first portion is used for the deter- 
mination of phosphoric acid. The acid is precipitated 
with ammonium molybdate. The second portion is 
used for determination of sulphuric acid, which is pre- 
cipitated as barium sulphate. The carbon dioxide 
is determined on a fresh portion of the original 
soil ; the acid is liberated with hydrochloric acid 
and the carbon dioxide is retained by absorbents and 
weighed. The nitrogen and humus are determined in 
separate portions of the original soil. 



Fig. 19. Diges- 
tion flask. 











;o 


o 








esidue. — K 

dried, ign 
andweigh( 
analyzed b 
sion proce; 


5' 

rD 


C/3 
O 

1— » 

a- 

Grq' 
rD 








o 


(V 






i-f,- IT) ►- 


s 


Cu 






3 &.n) 


r:) 






1 -t - -t 




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13 


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P 










r+ 






■ecipitate 

and ph( 
tate igni 
solved i 
iron de* 
phoric a 
a separa 
nal solu 
phosphc 
total giv 


US 

P3 ft 


p— ' 
o 












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P p ? *t:5 ^. 3 '■^- ., 3^ 3. 


3 '^ 


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w' 


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►-.X rt o 1^ Cli - x. 


ri) 3 
&.0 


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n' 






:Iron, alumina 
acid. Precipi- 
weighed. Dis- 
uric acid and 
The phos- 
termined from 
»n of the origi- 
im of iron and 
ubtracted from 
na. 


3* 
crq 


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etermin 

all otl: 
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;5 





76 SOILS AND FERTILIZERS 

89. Value of Soil Analysis. — Opinions differ as to 
the valne of soil analysis. It is claimed by some that 
a chemical analysis of a soil is of no practical value 
because it fails to give the amount of available plant 
food. A soil may have, for example, 0.4 per cent, of 
potash soluble in hydrochloric acid and still not 
contain sufficient available potash to produce a good 
crop, while another soil may contain 0.2 per cent, 
of potash soluble in hydrochloric acid and produce 
good crops. While these facts are frequently true, 
it does not necessarily follow that the chemical 
analysis of a soil is of no value because other sol- 
vents than hydrochloric acid may be used for soil 
analysis. Hydrochloric acid is used because it repre- 
sents the limit of the solvent power of plants. The 
figures obtained by the use of hydrochloric acid are 
valuable inasmuch as they indicate whenever an ele- 
ment is present in amounts which are too limited to 
admit of crop production. Suppose an ordinary soil 
contains 0.05 per cent, of acid-soluble potash, this 
would be too small an amount to produce good crops. 
The soil might contain 0.5 per cent, and yet not have 
a sufficient amount of available potash. Hence it is, 
that in interpreting results, the hydrochloric acid sol- 
vent may show when a soil is wholly deficient in any 
one element, as is sometimes the case, but it does not 
necessarily show a deficiency in the case of a soil rich 
in acid-soluble potash ; this can, however, be approx- 



FORMS OF PLANT FOOD 77 

imately indicated, by the use of other solvents, as ex- 
plained in section 90. 

The character of the soil, as acid, alkaline, or neu- 
tral should first be determined, because plant food ex- 
ists in a different form in each class of soils. If a soil 
contains from 0.3 to 0.5 per cent, or more of lime (as 
CaO) and from o.i to 0.4 per cent, of carbon dioxide 
(COJ, and is not strongly alkaline, there is a reason- 
able content of lime carbonate. If, however, the soil 
contains only o.oi or 0.02 per cent, of carbon dioxide, 
then the lime is not present as carbonate, but is prob- 
ably present as a silicate, in which case the soil may 
stand in need of a lime fertilizer. A soil which gives 
an alkaline or neutral reaction and contains 0.15 per 
cent, of phosphorus pentoxide, and is well supplied with 
organic matter and lime, is amply provided with phos- 
phoric acid, and under such conditions the exten- 
sive iise of phosphate fertilizers is not required, 
except possibly for special crops. Hilgard states that 
should the per cent, of phosphoric acid be as low as 
0.05, there is, in all probability, a poverty of this ele- 
ment. 

Soils containing less than 0.07 per cent, of total ni- 
trogen are usually deficient. A soil containing as 
high as o. 1 5 or o. 2 per cent, of nitrogen may fail to re- 
spond to crop production. Such cases are generally 
due to some abnormal condition of the soil, as a lack 
of alkaline compounds which are necessary for nitri- 



78 SOILS AND FERTILIZERS 

fication. The appearance of the crop is the best indi- 
cation as to a deficiency of nitrogen. 

A soil which contains less than 0.15 per cent, of pot- 
ash soluble in hydrochloric acid is quite apt to be de- 
ficient. Soils which contain 0.5 per cent, or more of 
lime carbonate will produce good crops on a smaller 
working supply of potash than soils which are poverty- 
stricken in lime. As a rule the best agricultural soils 
contain from 0.3 to 0.6 per cent, of potash. Sandy 
soils of good depth may contain less plant food than 
the figures given, and not be in need of fertilizers. 

The term volatile matter is sometimes confused with 
the term organic matter. The volatile matter includes 
the organic matter and the water which is held in 
chemical combination as in the hydrated silicates. 
A soil may have a high per cent, of volatile matter 
and contain very little organic matter. Indeed all 
clays contain from 5 to 9 per cent, of water of hydra- 
tion. The per cent, of humus, as will be explained 
in the next chapter, does not represent all of the or- 
ganic matter. 

The best results are obtained from soil analyses 
when an extended study is made of the soils of a lo- 
cality. Then an unknown soil of that locality can be 
compared with a productive soil of known composition. 
An isolated soil analysis, like an isolated analysis of 
well water, frequently fails in its object because of a 
lack of proper normal standards for comparison. 



FORMS OF PLANT FOOD 79 

When extended series of soil analyses have been made, 
much valuable information has been obtained. 

Suppose a soil contains 0.40 per cent, of acid-soluble 
potash and field experiments indicate that there is a 
deficiency of available potash. This may be due to 
some abnormal condition of the soil, as an insufficient 
amount of other alkaline compounds as calcium car- 
bonate to take the place of the potash which has been 
withdrawn by the crop, in which case the deficiency 
of potash could be remedied without purchasing solu- 
ble potash fertilizer, to become insoluble by fixation 
processes. If a soil contains only 0.04 per cent, of 
acid-soluble potash, the purchasing of potash fertili- 
zers would be more necessary, but with 0.40 per cent, 
of acid-soluble potash the way is open to render 
this potash available for crops. The various ways of 
rendering acid-insoluble potash and other compounds 
available for crop production, as by rotation of crops, 
use of farm manures, use of lime and green manures, 
or by different micthods of cultivation have not been 
sufficiently studied as yet to offer a solution to all of 
the problems of how to render inert plant food availa- 
ble. 

' 90. Action of Organic Acids upon Soils. — Dilute 
organic acids, as a one per cent, solution of citric acid, 
have been proposed as solvents for the determination 
of easily available plant food. It has been shown in 
the case of the Rothamsted soils which have produced 



8o SOILS AND FERTILIZERS 

50 crops of grain without manures, and which are 
markedly deficient in available phosphoric acid, that 
a I per cent, solution of citric acid dissolved only 0.003 
per cent, of phosphoric acid while the soil contained a 
total of 0.12 per cent. In the case of an adjoining 
plot which had received phosphate manures until the 
soil contained a sufficient amount of available phos- 
phoric acid to produce good crops, there was present 
0.03 per cent, of phosphoric acid soluble in a i per 
cent, citric acid solution.^^ 

Dilute organic acids are, to a certain extent, capable 
of showing deficiency of plant food. A soil which 
shows 0.03 per cent, of potash or phosphoric acid sol- 
uble in I per cent, citric acid is, as a rule, well stocked 
with available phosphoric acid. Prairie soils of high 
fertility yield from 0.03 to 0.05 per cent, of both pot- 
ash and phosphoric acid soluble in dilute organic 
acids ; soils which are deficient in these elements usu- 
ally contain less than o.oi per cent. 

The action of a single organic acid of specific 
strength cannot be taken as the measure of fer- 
tility for all soils and crops alike, because different 
plants do not have the same amount or kind of organic 
acid in the sap. Of the various organic acids, citric 
possesses the greatest solvent action upon lime, 
magnesia, and phosphoric acid, while oxalic acid has 
the strongest solvent action upon the silicates. Tar- 
taric acid appears to be less active as a solvent than 



FORMS OF PLANT FOOD 8 1 

either citric or oxalic acid. The combined use of 
dihite organic acids, as citric with hydrochloric acid of 
I.I 15 sp. gr., will generally give an accurate idea of 
the character of a soil. A fifth-normal solution of 
hydrochloric acid has also been proposed as a measure 
of the soil's active phosphoric acid, and has given 
satisfactory results. ^^ 

The use of dilute organic acids renders it possible 
to detect small amounts of readily soluble phosphoric 
acid and potash. It has been stated that when a soil 
has been manured a few years with a phosphate fertil- 
izer and brought into good condition as to available 
phosphoric acid, that a chemical analysis will fail to 
detect any difference in the soil before or after the 
treatment with fertilizer. In the case of hydrochloric 
acid as a solvent, this is true because an acre of soil 
to the depth of one foot weighs about 3,500,000 lbs. 
and 500 lbs. of phosphoric acid would increase the 
total amount of phosphoric acid about 0.015 per cent. 
When a dilute organic acid is used, only the more 
easily soluble phosphoric acid is dissolved, and this 
readily allows fertilized and unfertilized soils to be 
distinguished. The use of dilute organic acids and 
salts have shown a decided difference between soils 
fertilized and unfertilized with potash. -"^ 

91. Distribution of Plant Food. — In studying the 
chemical composition of a soil, the surface soil and 
the subsoil both require consideration. It frequently 



82 SOILS AND FERTILIZERS 

happens that the surface soil and the subsoil have en- 
tirely different chemical, as well as physical, properties. 
This is particularly true of the western prairie soils, 
where the surface soils generally contain less potash 
and lime, but more nitrogen and phosphoric acid, than 
the subsoils. When jointly considered the surface 
and subsoil have strong crop-producing powers, but if 
considered separately each would have weak points. 

Since crops appropriate their food mainly from the 
silt and clay particles, the amount of plant food pres- 
ent in these grades of particles determines largely the 
reserve fertility of the soil. A soil in which 70 per 
cent, of the total potash is present in the silt and clay, 
is in better condition for crop production than a sim- 
ilar soil with a like amount of potash which is present 
mainly in the sand. Because a soil has a given com- 
position, it does not follow that all of the different 
grades of particles have the same composition. In fact 
the different grades of soil particles may have as varied 
a composition as is met with among different soils.^^ 



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84 SOILS AND FERTILIZERS 

The figures under i give the composition of the 
particles, while under 2 are given the results calcu- 
lated on the basis of the total amount of each element. 
For example, the clay contains 1.47 per cent, of 
potash, while 50. 8 per cent, of the total potash of the 
soil is in the clay particles. 

A soil may contain a comparatively low per cent, of 
potash or phosphoric acid, mainly in the finer particles 
and evenly distributed so that the crop is better 
supplied with food than if more were present in 
the larger particles, unevenly distributed. The dis- 
tribution of the plant food in the soil has not been so 
extensively studied as the question of total plant food. 
Sometimes in judging the character of a soil from a 
chemical analysis, a soil fault, as lack of potash in the 
surface soil, is corrected by a high per cent, of 
the same element in the subsoil. The distribution of 
plant food in both surface soil and subsoil, as well 
as in the various grades of soil particles, is an im- 
portant factor of fertility. 

92. Composition of Typical Soils. — A few exam- 
ples are given, in tabular form, of the chemical compo- 
sition of soils from different regions in the United States. 
On account of variations in the same localities, the 
figures represent the composition of only limited areas 
of soils. There have been made in the United States 
a large number of soil analyses, which as yet have not 
been compiled nor studied in a systematic way. 



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FORMS OF PLANT FOOD 87 

93. Alkaline Soils. — When a soil contains such an 
excessive amount of alkaline salts as sodium sulphate, 
sodium or potassium carbonate or chloride, as to be 
destructive to vegetation, it is called an ' alkali ' 
soil. These soils are found in semi-arid regions, and 
wherever conditions have been such that the alka- 
line compounds have not been drained from the 
soil. Occasionally calcium chloride is the destructive 
material. Chlorine in any ordinary' combination is 
destructive to vegetation when present to the extent 
of more than i part per looo parts of soil. Of the 
various alkaline compounds potassium carbonate is one 
of the most injurious. Sodium sulphate is a milder 
form of alkali. When evaporation takes place the 
alkaline compounds are deposited as a coating on the 
surface of the soil. Many soils supposed to be strongly 
alkaline, because a white coating is formed on the 
surface, simply contain so much lime carbonate that a 
deposit is formed. Many excellent soils have been 
passed over as ' alkali ' soils when in reality they are 
limestone soils. 

94. Improving < Alkali' Soils. ^^ — When a large tract 
of alkali is to be brought under cultivation the amount 
of prevailing alkaline compounds should be determined 
by chemical analysis. It frequently happens that 
deep and thorough cultivation are all the treatment 
that is necessar^\ If the prevailing alkali is sodium 
carbonate a dressing of land plaster may be applied so 



88 SOII.S AND FERTILIZERS 

as to change the alkali from sodium carbonate to 
sodium sulphate, a less destructive form, the reaction 
being : 

Na CO H- CaSO = CaCO + Na SO . 

23 4 324 

Many shrubs, as greesewood, and weeds, as Russian 
thistle, take from the soil large amounts of alkaline 
matter, and it is sometimes advisable to remove a 
number of such crops so as to reduce the alkali. A 
slightly beneficial effect is sometimes noticed on small 
' alkali ' spots where the ashes from straw are used, 
forming potassium silicate. As a rule ashes are more 
injurious than beneficial, on an ' alkali' soil. Irrigation 
and thorough drainage, if continued long enough, will 
effect a permanent cure. Irrigation without drainage 
may cause a more alkaline condition by bringing to 
the surface subsoil alkali. The waters from some 
streams and wells are unsuited for irrigation on ac- 
count of containing too much alkaline matter. Mildly 
alkaline soils will usually repay in crop production all 
the labor which is expended in making them pro- 
ductive, and when brought under cultivation are fre- 
quently very fertile soils. A small amount of alkaline 
compounds in a soil is beneficial ; in fact, many soils 
would be more productive if they contained more 
alkaline matter. 

95. Improving Small Tracts of ^Alkali' Land. — 
When the places are located so that they can be under- 
drained at comparatively little expense, this should be 



FORMS OF PLANT FOOD 89 

done, as it will prove the best and most permanent 
way of removing the alkali. Good surface drainage 
should also be provided. Quite frequently a quarter 
or a third of the total alkali in the soil will, in a dry 
time, be found near and on the surface. In such cases, 
and if the spots are small, a large amount of alkali 
can be removed by scraping the surface and then cart- 
ing the scrapings away and dumping them where 
they can do no damage. 

When preparing an 'alkali' spot for a crop, deep 
plowing should be practiced, so as to open up the soil 
and remove the excess of alkaline matter from the 
surface. Where manure, particularly horse manure, 
can be obtained these spots should be manured very 
heavily. The horse manure, when it decomposes, fur- 
nishes acid products, which combine with the alkaline 
salts. The manure also prevents rapid surface evapora- 
tion. Oats are about the safest grain crop to seed on 
an ' alkali ' spot because the oat plant is capable of thri- 
ving in an alkaline soil where many other grain crops 
fail. 

'Alkali' soils are usually deficient in available 
nitrogen. The organism which carries on the work 
of changing the humus nitrogen to available forms 
cannot thrive in a strong alkaline solution. In many 
oT these soils, as demonstrated in the laboratory, nitri- 
fication cannot take place. After thorough drainage and 
preparation for a crop, a few loads of good soil from a 



go SOILS AND FERTILIZERS 

fertile field sprinkled on ' alkali ' spots will do much to 
encourage nitrification, by introducing the nitrifying 
organisms. 

THE ORGANIC COMPOUNDS OF SOILS 

96. Sources of the Organic Compounds of Soils. 

— The organic compounds of soils are derived from 
accumulated vegetable and animal matter which has 
been acted upon by micro-organisms. The organic 
matter of the soil originally consisted of the same 
compounds, as cellulose, proteid bodies, and organic 
acids that are found in living plants and animals. By 
the action of various micro-organisms the cellulose, 
proteid bodies, and other compounds have undergone 
chemical changes, and produced the organic com- 
pounds of the soil which are mixtures of animal and 
vegetable matter in various states of decomposition. 
The organic compounds of the soil may exist in 
various forms ranging from cellulose to the final oxi- 
dation products as carbon dioxide and water. ^^ 

97. Classification of the Organic Compounds. — 

Various attempts have been made to classify the or- 
ganic compounds of the soil, but those which have 
been described are without doubt mixtures of various 
bodies, and not distinct compounds. An old classifi- 
cation by Miilder^^ was humic, ulmic, crenic, and ap- 
procrenic acids. This classification does not include 
any nitrogenous inatter containing more than four per 
cent, nitrogen, while organic matter with eight to ten 



ORGANIC COMPOUNDS OF SOILS 9I 

per cent, and in some cases eighteen per cent, of 
nitrogen is quite frequently met with ; hence this 
classification is incoiuplete as it includes only a part of 
the organic compounds of the soil. 

98. Humus. — The term humus is employed to 
designate what are considered to be the most active 
principles of the organic compounds. Humus is the 
animal or vegetable matter of the soil in intermediate 
forms of decomposition. From different soils, it is ex- 
tremely varied in composition : in one soil it may 
have been derived mainly from cellulose, while in an- 
other it may have been derived from a inixture of cel- 
lulose, proteid bodies, and other organic compounds. 
The term humus, unless qualified, is a very indefinite 
one. The humus given in the analyses of soils is ob- 
tained by extracting the soil with a dilute alkali as 
ammonium hydroxide, after treating the soil with a 
dilute acid to remove the lime which renders the 
humus insoluble. 

99. Humification, and Humates. — When the ani- 
mal and vegetable matter incorporated into soils un- 
dergoes decomposition there is a union of the organic 
compounds and the base-forming elements of the soil. 
The decaying organic matter produces organic prod- 
ucts of an acid nature. The organic acids and the 
base-forming products unite to form humates or or- 
ganic salts, which are neutral bodies. This process is 
humification. '7 



92 SOILS AND FERTILIZERS 

Humic acid + calcium carbonate = calcium humate + CO2. 
Humic acid + potassium sulphate = potassium humate, etc. 

The fact that a union occurs between the organic 
matter and the soil has been demonstrated by mixing 
with soils known amounts of various organic materials, 
as cow manure, green clover, meat scraps, and saw- 
dust, and allowing humification to go on for a year or 
more. After humification has taken place, the humus 
extracted from the soil contains more potash, phos- 
phoric acid, and other elements than were present in 
the humus of the original soil and humus-forming 
material, showing that a chemical union has taken 
place bet\^een the decaying organic matter and the soil. 
The power of various organic substances to produce 
humates is illustrated in the followino- table :^9 

o 

Humic phos- Humic 

^ , phoric acid. potash 

Low manure htimus : Grams. Grams. 

In original manure and soil 1.17 1.06 

In final humus product (after hu- 
mification) 1.62 1.27 

Gain in humic forms 0.45 0.21 

Green clover humus : 

In original soil and clover 3.21 5.26 

In final humus product 3.74 4.93 

Gain in humic forms 0.53 ( Loss) 0.33 

Meat scrap humus : 

In original meat scraps and soil. . 1.07 0.25 

In final humus product 1.18 0.36 

Gain o. 11 o.ii 



ORGANIC COMPOUNDS OF SOILS 93 

Humic phos- Humic 

phoric acid. potash. 

Sawdust humus : Grams. Grams. 

In original sawdust and soil 0.85 0.67 

In final humus product 0.78 0.70 

Oat straw luinius : 

In original straw and soil 1.02 2,42 

In final humus product i .03 2.41 

100. Comparative Value and Composition of Hu- 
mates. — The humus produced from nitrogenous 
bodies, as meat scraps, is more vaUiable than that pro- 
duced from cellulose bodies as sawdust, because the 
former have a greater power of combining with the 
phosphoric acid and potash of the soil. The non- 
nitrogenous compounds, as cellulose, starch, and sugar, 
undergo fermentation but seem to possess little, if any, 
power to form humates. There is also a great differ- 
ence in soils as to their humus-producing powers. 
Soils deficient in lime or alkaline compounds possess 
only a feeble power to produce humates. There is 
also a marked variation in the composition of the 
humus produced from different kinds of organic matter. 
Straw, sawdust, and sugar, materials rich in cellulose 
and other carbohydrates, yield a humus characteris- 
tically rich in carbon and poor in nitrogen. Materials 
rich in nitrogen, like meat scraps, green clover, and 
manure, produce a more valuable humus, rich in nitro- 
gen and possessing the power to combine with the 
potash and phosphoric acid of the soil to form 
humates. 



94 SOILS AND FERTILIZERS 

Compos [TioN of Humus Produced by^^ 

Cow Green Meat Wheat Oat Saw- 

niauure. clover, scraps, flour, straw. dust. Sugar. 

Carbon 41.95 54.22 4S.77 51.02 54.30 49.28 57.84 

Hydrogen 6.26 3.40 4.30 3.82 2.48 3.33 3.04 

Nitrogen 6.16 8.24 10.96 5.02 2.50 0.32 0.08 

Oxygen 45.63 34.14 35.97 40.14 40.72 47.07 39.04 

Total 100.00 100.00 loo.co 100.00 100.00 100.00 100.00 

Highest. I.owest. Difference. 

Carbon 57-84 Sugar 41-95 Cow manure- • • 15.89 

Hydrogen ... 6.26 Cow manure . 2.48 Oat straw 3.78 

Nitrogen 10.96 Meat scraps.. 0.08 Sugar 10.88 

Oxygen 47-07 Sawdust 34-14 Green clover. . . 12.93 

The differences in composition are noticeable. The 
humus produced by each material as green clover, oat 
straw, or sawdust is different from that produced by 
any other material. The humus from green clover is 
undoubtedly very complex in nature, because it con- 
tains both nitrogenous and non-nitrogenous com- 
pounds, and each class has a different action in humi- 
fication processes, hence it follows that the humus 
from the green clover must be a complex mixture of 
both nitrogenous and non-nitrogenous bodies. 

The nature of the humus, whether nitrogenous or 
non-nitrogenous, is important. Humus produced from 
sawdust and humus from meat scraps may be taken 
respectively as types of non-nitrogenous and nitrog- 
enous humus. 

loi. Value of Humates as Plant Food. — Various 
opinions have been held regarding the actual value, 



ORGANIC COMPOUNDS OF SOILS 95 

as plant food, of this product from partially decayed 
animal and vegetable matter. Humus was formerly 
regarded as composed only of carbon, hydrogen, and 
oxygen, and inasmuch as plants obtain these elements 
from water and from the carbon dioxide of the air, no 
value was assigned to humus. Later investigators 
added nitrogen to the list but stated that the nitrogen, 
when combined with the humus and before under- 
going fermentation, was of no value as plant food. 

Recent investigations have proved that the phos- 
phoric acid and other mineral elements combined 
with the organic matter of soils are of value as plant 
food,'^ and it has been demonstrated that crops grown 
on the black soils of Russia obtain a large part of 
their mineral food from organic combinations. ^3 cul- 
ture experiments have shown that under normal 
conditions plants like oats and rye may obtain their 
mineral food entirely from humate sources. Seeds 
when planted in a mixture of pure sand and neu- 
tral humates from fertile soils, produced normal 
plants. In order to secure the best conditions 
for growth, a little lime must be present to prevent 
the formation of humic acid, and the usual organisms 
found in fertile fields must also be introduced. The 
following example is given of oats grown under such 
conditions : 



96 SOILS AND FERTILIZERS 

Nitrogen and Ash EivEmknts.'*^ 

In six oat In six mature 

seeds. plants. 

Gram. Gram. 

Nitrogen 0.0040 0.0556 

Potash 0.0013 0,0640 

Soda o.oooi -^ 0079 

Lime 0.0002 0.0249 

Magnesia 0.0005 o.oi 10 

Iron 0.0064 

Phosphoric anhydride 0.0016 0.0960 

Sulphuric anhydride 0.0001 0.0090 

SiHcon 0.0026 0.7300 

The fact that plants feed on humate compounds, 
and that decaying animal and vegetable matter pro- 
duce humates from the inert potash and phosphoric 
acid of the soil, has an important bearing upon crop 
production, because it indicates a way by which inert 
plant food may be converted into more active forms. 
It also explains that stable manure is valuable because 
it makes the inert plant food of the soil more available. 

102. Amount of Plant Food in Humate Forms. — 
In a prairie soil containing three and five-tenths per 
cent, of humus there are present 100,000 pounds of 
humus per acre. Combined with this humus there 
are from 1,000 to 1,500 pounds each of phosphoric 
acid and potash. Soils which have been under long 
cultivation without the restoration of any humus 
contain from 300 to 500 pounds each of humic potash 
and phosphoric acid.'^ A decline in crop-producing 
power has in many cases been brought about by the 
destruction of the humus. 



ORGANIC COMPOUNDS OF SOILS 97 

103. Loss of Humus. — The loss of humus from the 
soil is caused by oxidation and by fires. Any method 
of cultivation which accelerates oxidation reduces the 
humus content. In many of the western prairie soils 
which have been under continuous grain cultivation 
for thirty years and more, the amount of humus has 
been reduced one-half. Summer fallowing also causes 
a loss of humus. When land is continually under 
the plow, and no manures are used, the humus is 
rapidly oxidized, and there is left, in the soil, organic 
matter w^hich is slow to decay. 

Forest and prairie fires have been very destructive 
to the organic compounds of the soil. A soil from 
Hinckley, Minn., before the great forest fire of 1893 
showed 1.69 per cent, humus and 0.12 per cent, 
nitrogen. '7 After the fire there were present 0.41 
per cent, humus and 0.03 per cent, nitrogen. The 
forest fire caused a loss of 2,500 pounds of nitrogen 
per acre. In clearing new land, particularly forest 
land, there is frequently an unnecessary destruction of 
humus materials. Instead of burninor all of the ve^e- 
table matter it would be better economy to leave some 
in piles for future use as manure. When all of the 
vegetable matter has been burned two or three good 
crops are obtained but the permanent crop-producing 
power of the land is reduced because of the loss 
of nitrogen. When the vegetable matter has been 
only partially removed the crops at first may be 



98 SOILS AND FERTILIZERS 

smaller, but in a few years returns will be greater than 
if all of the vegetable matter were burned. 

104. Physical Properties of Soils Influenced by- 
Humus . — The physical properties of a soil may be 
entirely changed by the addition or the loss of humus. 
The influence of humus upon the weight, color, 
water, and heat of soils, is discussed in the chapter on 
the physical properties of soils. Soils reduced in 
humus content have less power of storing up water 
and resisting drought. This fact is illustrated in the 
following table :^° 

Per Cent. Water. 

After 10 hours 
exposure in 
In soil. tray, to sun. 

Soil rich in humus (3.75 per cent.) 16.48 6.12 

Adjoining soil poorer in humus (2.50 per cent.) 12.14 3-94 

105. Humic Acid. — In the absence of calcium 
carbonate or other alkaline compounds, the vegetable 
matter may produce acid products destructive to the 
growth of some crops. The acidity in such cases may 
be readily corrected by the use of lime or wood ashes. 
Studies conducted by the Rhode Island Experiment 
Station indicate that the areas of acid soils are 
quite extensive. Acid soils can be distinguished by 
their action upon red litmus paper. A soil may, how- 
ever, give an acid reaction and contain a fair amount 
of lime. The subject of acid soils and liming is consid- 
ered in Chapter IX. 



ORGANIC COMPOUNDS OF SOILS 



99 



io6. Soils in Need of Humus. — Sandy and sandy 
loam soils that have been cultivated for a number of 
years to corn, potatoes, and small grains, without the 
use of stable manures or the proper rotation of crops, 
are deficient in humus. Clay soils, as a rule, do not 
stand in need of humus so much as loam or sandy 
soils. The mechanical condition of heavy clays is, 




Fig. 20. Humus from old soil. 




Fig. 2 1 . Humus from new soil . 



however, improved by the addition of humus-forming 
material. 'Alkali' soils are usually deficient in humus. 
Its addition to loam or sandy soils is beneficial in pre- 
\'enting the soil from drifting because humus binds 
together the soil particles. There are but few soils, 
under ordinary cultivation, to which it is not safe to 
add humus-forming materials. Ordinary prairie soils, 
for the first ten years after breaking, are usually well 



lOO SOILS AND FERTILIZERS 

supplied. Swampy, peaty, and muck soils contain 
large amounts ; in fact, they are often overstocked 
with humus. 

107. Active and Inactive Humus. — When soil has 
been under long cultivation, and no manures have 
been used, the nitrogen and mineral matters combined 
with the humus are reduced. The humus from long 
cultivated fields contains a higher per cent, of carbon 
than that from well-manured or new land ; it is also 
less active because of the higher per cent, of carbon 
which does not readily undergo oxidation. '^ 

Humus from Huiuus from 

new soil. old soil. 

Per cent. Per cent. 

Carbon 44.12 50.10 

Hydrogen 6.00 4.80 

Oxygen 35. 16 33.70 

Nitrogen 8.12 6.50 

Ash 6.60 4.90 

Total humus material ••5.30 3.38 

108. Influence of Different Methods of Farming 
upon Humus. — The general system of farming has a 
direct effect upon the humus content and composition 
of the soil. Where live stock is kept, the manure 
properly used, and the crops systematically rotated, 
the crop-producing power of the land is not decreased, 
as in the case of the one-crop system. The influence 
of different systems of farming upon the humus con- 
tent and other properties of the soil may be observed 
from the following table :3° 



ORGANIC COMPOUNDS OF SOILS TGI 

Phos- 
phoric 
acid com- Water- 
bined holding 
Weight Humus. Nitrogen, with capac- 
per cu. Per Per humus. ity. 

Character of soil. ft. lbs. cent. cent. Per cent. Per cent. 

1. Cultivated thirty -five years ; 
rotation of crops and manure; 

high state of productiveness. 70 3.32 0.30 0.04 48 

2. Originally same as i ; con- 
tinuous grain cropping for 
thirty-five years ; low state of 

productiveness 72 1.80 0.16 o.oi 39 

3. Cultivated forty -two years ; 
systematic rotation and ma- 
nure ; good state of product- 
iveness 70 3-46 0.26 0.03 59 

4. Originally same as 3 ; culti- 
vated thirty -five years; no 
systematic rotation or ma- 
nure ; medium state of pro- 
ductiveness 67 2.45 0.21 0.03 57 



CHAPTER IV 



NITROGEN OF THE SOIL AND AIR, NITRIFICATION, AND 
NITROGENOUS MANURES 

109. Importance of Nitrogen as a Plant Food. — 

The illustration (Fig. 22) shows an oat plant which has 
received no nitrogen, while potash, phosphates, lime, and 
all other essential elements of plant food 
were liberally supplied. Observe the pe- 
culiar and restricted growth, with but little 
root development. The leaves were yel- 
lowish in color. 

In the absence of nitrogen a plant 
makes no appreciable growth. With only 
a limited supply, a plant begins its growth 
in a normal way but as soon as the avail- 
able nitrogen is used up, the lower and 
smaller leaves begin gradually to die 
down from the tips, and all of the plant's 
energy is centered in one or two leaves. 
In one experiment when only a small 
amount of nitrogen was supplied, the plant 
struggled along in this way for about nine 
weeks, making a total growth of but six 
and one-half inches.'^ Just at the critical point 
when the plant was dying of nitrogen starvation, 
a few milligrams of calcium nitrate were given. In 




Fig. 22. Oat 
plant grown 
without nitro- 
gen. 



NITROGEN ^S A PLANT FOOD IO3 

thirty-six hours the plant showed signs of renewed 
life, the leaves assumed a deeper green, a new grow^th 
was begun, and finally four seeds were produced. 
During the time of seed formation more nitrogen w^as 
added, but with no beneficial result. All of the 
essential elements for plant growth were liberally pro- 
vided, except nitrogen which Avas very sparingly sup- 
plied at first, until near the period of seed formation, 
when it was more liberally supplied. 

When plants have reached a certain period in their 
development, and have been starved for the want of 
nitrogen, the later application of this element does not 
produce normal growth, as the energies of the plant 
have been used up in searching for food. Nitrogen, as 
well as potash, lime, and phosphoric acid, are all neces- 
sary while plants are in their first stages of growth. 

In the case of wheat, nitrogen is assimilated more 
rapidly than are any of the mineral elements. Before 
the plant heads out, over eighty-five per cent, of the 
total nitrogen required has been taken from the soil. 3^ 
Corn also takes up all of its nitrogen from four to five 
weeks before the crop matures. Flax takes up 
seventy-five per cent, of its nitrogen during the first 
fifty days of growth. 37 

Nitrogen is demanded by all crops. It forms the 
chief building material for the proteids of all plants. 
In the absence of a sufficient amount of nitrogen, the 
rich green color is not developed ; the foliage is of a 
yellowish tinge. Nitrogen is one of the constituents 



I04 SOILS AND FERTILIZERS 

of chlorophyl, the green coloring-matter of plants, 
hence with a lack of nitrogen only a limited amount 
of chlorophyl can be produced. Plants with large, 
well-developed leaves of a rich, green color are not 
suffering for nitrogen. Nitrogenous fertilizers have 
a tendency to produce a luxurious growth of foliage 
deep green in color. 

ATMOSPHERIC NITROGEN AS A SOURCE OF PLANT FOOD 

110. Early Views. — In addition to the carbon, hy- 
drogen, and ox}'gen, which form the organic com- 
pounds of- plants, nitrogen also, at the beginning of 
the present century, was known to be present. The 
sources of carbon, hydrogen, and oxygen, for crop 
purposes, were much easier to determine and under- 
stand than the sources of nitrogen. Priestley, the dis- 
coverer of oxygen, believed that the free nitrogen of 
the air was a factor in supplying plant food. De SaUvS- 
sure arrived at just the opposite conclusion. The facts 
which led to these beliefs were not convincing because 
the methods of chemical analysis had not yet been 
sufficiently perfected to solve the question. 3^ 

111. Boussingault's First Experiments. — Boussin- 
gault was the first to make a careful study of the sub- 
ject. In a prepared soil, free from nitrogen, and con- 
taining all of the other elements necessary for plant 
growth, he grew clover, wheat, and peas, carefully 
determining the nitrogen in the seed. The plants 
were allowed free access to the air, being simply pro- 



ATMOSPHERIC NITROGEN 



105 



tected from dust, and were watered with distilled 
water. But little growth was made. At the end of 
two months the plants were submitted to chemical 
analysis, and the amount of nitrogen present was 
determined. 

His first results are eiven in the followino- talkie :39 



Nitrogen. 

lu seed sown. 
Gram. 

Clover, 2 nios o. 1 1 



In plant. 
Gram. 



Gain. 
Gram. 



Wheat 2 " 

" 3 " 
Peas 2 ' ' 

Boussino-ault 



0.12 

0.156 

0.04 

0.06 

o. 10 



O.OI 

0.042 

^.003 

0.003 

0.053 
when plants, in a 



o. 114 

0.043 

0.057 

0.047 

concluded that 
sterile soil, were exposed to the air, there was with 
some a slight gain of nitrogen but 
the amount gained from atmospheric 
sources was not sufficient to feed the 
plant and allow it to reach full ma- 
turity. By many these results were 
not accepted as conclusive. 

112. Boussingault's Second Ex- 
periments. — Fifteen years later 
(1853) Boussingault repeated his ex- 
periments in a different way. The 
plants were grown in a large carboy 
with a limited volume of air so as to^^g- 23- Plants grown 

rv 11 r • ^^ carboy. 

cut on all sources of combined nitro- 




gen, as ammonia. 



Bv 



means of a second glass vessel 



I06 SOILS AND FERTILIZERS 

{b^ Fig. 23) the carboy was kept supplied with a 
liberal amount of carbon dioxide, so that plant growth 
would not be checked for lack of this material. When 
experiments were carried on in this way using a fertile 
soil, the plants reached full maturity, but when a soil 
free from nitrogen was used, plant growth was soon 
checked. A general summary of this work is given in 
the following table : 39 

Nitrogen. 

In seeds. In plant. I^oss. 

Gram. Gram. Gram. 

Dwarf beans o.iooi 0.0977 — 0.0024 

Oats 0.0109 0.0097 — 0.0012 

White lupines 0.2710 0.2669 — 0.0041 

Garden cress 0,0013 0.0013 

These experiments show that with a sterilized soil, 
and all sources of combined atmospheric nitrogen cut 
off, the free nitrogen of the air takes no part in the 
food supply of the plant. 

113. Boussingault's Third Experiments. — In 1854 
Boussingault again repeated his experiments; this 
time he grew the plants in a glass case so constructed 
that there was a free circulation of air from which all 
combined nitrogen had been removed. These exper- 
iments were similar to his second series ; the plants, 
however, were not grown in a limited volume of air. 
The results, without going into detail, showed that 
the free nitrogen of the air, under the conditions of the 
experiment, took no part in the food supply of plants. 



ATMOSPHERIC NITROGEN IO7 

If anything, there was less nitrogen recovered in the 
dwarfed plants than there was in the seed sown. 

114. Vine's Results. — About the same time Ville 
carried on a series of experiments of like nature, but 
in a different way, and arrived at just the opposite 
conclusions. In short, his experiments indicated that 
plants were capable of making liberal use of the free 
nitrogen of the air for food purposes. The directly 
opposite conclusions of Boussingault and Ville, led to 
a great deal of controversy. The French Academy of 
Science took up the question, and appointed a commis- 
sion to review the work of Ville. The commission 
consisted of six prominent scientists. They reported 
that "M. Ville's conclusions are consistent with his 
labor and results." ^^ 

115. Work of Lawes and Gilbert. — Lawes and 
Gilbert, however, carried on such extensive exper- 
iments under a variety of conditions as to remove all 
doubt regarding the question. Plants were grown in 
sterilized soils, in prepared pumice stone, and in soils 
wdth a limited and known quantity of nitrogen beyond 
that contained in the seed. Different kinds of plants 
were experimented with. The work was carried on 
with the utmost care and with apparatus so constructed 
as to eliminate all controllable factors. The results in 
the aggregate clearly indicate that plants, when acting in 
a sterile medium, are unable to make use of the free nitro- 
gen of the air for the production of organic matter. 3^ 



I08 SOILS AND FERTILIZERS 

1 16. Atwater's Experiments. — Atwater carried on 
similar experiments in this conntry.4° Some of his 
resnlts indicate that when seeds germinate they lose a 
small part of their nitrogen, and when grown in a 
sterile soil, they fail to fix any of the free nitrogen of 
the air. 

In all of the work of the different investigators prior 
to 1888, plants were grown in a sterilized medium, 
and under these conditions they are unable to make 
use of the free nitrogen of the air. 

117. Field and Laboratory Tests. — Experiments 
with sterilized soils do not represent the normal 
conditions of growing crops, where all of the 
bacteriological agencies of the soil, the air, and the 
plant, are free to act. Experiments have shown that 
these agencies have an important bearing upon plant 
growth. 

In a five years' rotation of clover and other legu- 
minous plants, Lawes and Gilbert found that a soil 
gained from two to four hundred pounds of nitrogen 
in addition to that removed in the crop, while land 
which produced wheat continuously had gradually 
lost nitrogen. The amount in the subsoil remained 
nearly the same. All of these facts plainly indicated 
that crops like clover have the power of gaining 
nitrogen from unknown sources. The results of 
prominent German agriculturists led to the same con- 
clusion. It was known that wheat grown after clover 



ATMOSPHERIC NITROGEN IO9 

gave as good results as the use of nitrogenous manure 
for the wheat, but for many years this fact was unex- 
plained. 

118. HellriegePs Experiments. — He grew legu- 
minous plants in nitrogen-free soils. One set of plants 
was watered with distilled water, while another had in 
addition small amounts of leachings from an old loam 
field. The plants watered with distilled w^ater alone 
made but little growth, while those watered with the 
loam leachings reached full maturity and contained 
something like a hundred times more nitrogen than 
was in the seed sown. The dark green color was also 
developed, showing the presence of a normal amount 
of chlorophyl. The roots of the plants had well- 
developed swellings or nodules, while those that were 
watered with distilled water alone had none. The 
loam leachings contained onlv a trace of nitroo^en.^^ 

119. Experiments of Wilfarth. — Experiments by 
Wilfarth give more exact data regarding the amount 
of nitrogen taken from the air. Lupines w^ere grown 
in the same way, and one lot watered with distilled 
water, while another lot received in addition leachings 
from an old lupine field. 

Watered with distilled water. Watered with soil leachings. 

Dry matter. Nitrogen. Dry matter. Nitrogen. 

Grams. Gram. Grams. Grams. 



0.919 


0.015 


44.72 


r.099 


0.800 


0.014 


45.61 


1-153 


0.921 


0.013 


44-48 


I -195 


1.021 


0.013 


42.45 


1-337 



no SOILS AND FERTILIZERS 

These experiments have been verified by many 
other investigators until the fact has been established 
that leguminous plants may, through the agency of 
micro-organisms, make use of the free nitrogen of the 
air. The work of Hellriegel was not accidental but 
the result of careful and systematic investigation. As 
early as 1863 ^^ observed that clover would develop 
along the roadway in sand in which there was scarcely 
a trace of combined nitrogen. 

120. Composition of Root Nodules. — The root 
nodules referred to, are particularly rich in nitrogen. 
In one experiment, the light-colored and active ones 
contained 5.55 per cent, of nitrogen while the dark- 
colored and older ones contained 3.21 per cent. The 
entire nodules of the root both active and inactive 
contained 4.60 per cent, nitrogen. The root itself 
contained 2.21 per cent, nitrogen. ^^ 

The root nodules also contain definite and charac- 
teristic micro-organisms, and it was the spores of these 
organisms that were present in the soil extract in both 
Hellriegel's and Wilfarth's experiments. In the ster- 
ilized soils they were not present. These organisms 
found in root nodules, are the essential agents which 
aid in the fixation of the free nitrogen of the air, and 
in its ultimate use as plant food. 

121. Nitrogen in the Root Nodules Returned to 
the Soil. — Ward has shown that when clover roots 
decay, the organisms and nitrogen present in the nod- 



NITROGEN COMPOUNDS OF THE SOIL III 

ules are distributed within the soil. 3^ Hence when- 
ever a leguniinous crop is raised, nitrogen is added to 
the soil, instead of being taken away, as in the case of 
a grain crop. The amount of nitrogen per acre 
returned to the soil by a leguminous crop as clover, 
varies with the growth of the crop. In the roots of a 
clover crop a year old there are present from 20 to 30 
pounds of nitrogen per acre, while in the roots and 
culms of a dense clover sod, two or three years old, 
there may be present 75 pounds or more of nitrogen. 
Peas, beans, lucern, cow peas, and all members of the 
leguminous family possess the power of fixing the free 
nitrogen of the air by means of micro-organisms. 
The micro-organisms associated with one species as 
clover differ from these associated with another as 
lucern. The amount of nitrogen which the various 
legumes return to the soil is variable. Hellriegel's re- 
sults are of the greatest importance to agriculture 
because they show how the free nitrogen of the air can 
be utilized indirectly as food, by crops unable to appro- 
priate it for themselves. 

THE NITROGEN COMPOUNDS OF THE SOIL 

122. Origin of the Soil Nitrogen. — The nitrogen of 
the soil is derived chiefly from the accumulated re- 
mains of animal and vegetable matter. The original 
source of the soil nitrogen, that is the nitrogen which 
furnished food to support the vegetation from which 
our present stock of soil nitrogen is obtained, was 



112 SOILS AND FERTILIZERS 

probably the free nitrogen of the air. All of the 
ways in which the free nitrogen of the air has been 
made available to plants of higher orders which reqnire 
combined nitrogen, are not known. It is supposed, 
however, that this has been brought about by the 
workings of lower forms of plant life, and by micro- 
organisms. Whatever these agencies have been they 
do not appear to be active in a soil under high cultiva- 
tion, because the tendency of ordinary cropping is to 
reduce the supply of soil nitrogen. 

123. Organic Nitrogen of the Soil. — In ordinary 
soils the nitrogen is present mainly in organic 
forms combined with the carbon, hydrogen, and 
oxygen; and to a less extent with the mineral ele- 
ments forming nitrates. The organic forms of 
nitrogen, it is generally considered, are incapable of 
supplying plants with nitrogen for food purposes until 
the process known as nitrification takes place. The 
nitrogenous organic compounds in cultivated soils are 
derived mainly from the undigested protein compounds 
of manure and from the nitrogenous compounds in 
crop residues. When decomposition occurs, amides, 
organic salts, and other allied bodies are without 
doubt produced as intermediate products before nitrifi- 
cation takes place. The organic nitrogen of the soil 
may be present in exceedingly inert forms similar to 
leather. In fact in many peaty soils there are large 
amounts of inactive organic compounds rich in 



NITROGEN COMPOUNDS OF THE SOIL II 3 

nitrogen. In other soils the nitrogen is present in 
less complex forms. The organic nitrogen of the soil 
may vary in complexity from forms like the nitrogen 
of urea to forms like that of peat. 

124. Amount of Nitrogen in Soils. — The fertility 
of any soil is dependent, to a great extent, upon the 
amount and form of its nitrogen. In soils of the 
highest degree of fertility there is usually present 
from 0.2 to 0.3 per cent, of total nitrogen, equivalent 
to from 7,000 to 10,000 pounds per acre to the depth 
of one foot. Many soils of good crop-producing 
power contain as low as 0.12 per cent, of nitrogen. 
There is usually two or three times more nitrogen in 
the surface soil than in the subsoil. In many sandy 
soils which have been allowed to decline in fertility 
the nitrogen may be less than 0.04 per cent. Of the 
total nitrogen in soils there is rarely more than 2 per 
cent, at any one time, in forms available as plant 
food.43 A soil with 5,000 pounds of total nitrogen 
per acre would contain about 100 pounds of available 
nitrogen of which only a part comes in contact with 
the roots of crops. Hence it is that a soil may con- 
tain a large amount of total nitrogen and yet be defi- 
cient in available nitrogen. 

125. Amount of Nitrogen Removed in Crops. 

— The amount of nitrogen removed in crops ranges 
from 25 to 100 pounds per acre depending upon the 
nature of the crop. It does not necessarily follow that 



114 SOILS AND FERTILIZERS 

the crop which removes the largest amount of nitrogen 
leaves the land in the most impoverished condition. 
Wheat and many grains, while they do not remove 
such a large amount of nitrogen in the crop, leave 
the soil more exhaused than if other crops were grown. 
This, as will be explained, is caused by the loss of 
nitrogen from the soil in other ways than through the 
crop. 



37 



Pounds of nitrogen 
per acre. 

Wheat, 20 bushels 25 

Straw, 2000 pounds 10 

Total .^ V 35 

Barley, 40 bushels 28 

Straw, 3000 pounds 12 

Total 40 

Oats, 50 bushels 35 

Straw, 3000 pounds 15 

Total 50 

Flax, 15 bushels 39 

Straw, 1800 pounds 15 

Total 54 

Potatoes, 150 bushels 40 

Corn, 65 bushels 4" 

Stalks, 3000 pounds ; 35 

Total 75 

126. Nitrates and Nitrites. — The amount of nitro- 
gen in the form of nitrates and nitrites, varies from 
mere traces to 150 pounds per acre. Calcium nitrate 



NITROGEN COMPOUNDS OF THE SOIL II5 

is the usual form met with, especially in soils which 
are sufficiently supplied with calcium carbonate to 
allow nitrification to progress rapidly. Nitrates and 
nitrites are the most valuable forms of nitrogen for 
plant food. Both are produced from the organic 
nitrogen of the soil. A nitrate is a compound com- 
posed of a base element as sodium, potassium, or 
calcium, combined with nitrogen and oxygen. A 
nitrite contains less oxygen than a nitrate. 

Potassium nitrate, KNO^, sodium nitrate, NaNO , 
and calcium nitrate, Ca(NO )^^ are the nitrates which 
are of most importance in agriculture. The nitrites, 
as potassium nitrite, KNO^, are met with to a less 
extent than the nitrates. Nitrates and nitrites are 
present in surface well waters contaminated with 
animal and vegetable matter. Many well waters 
possess some material value as a fertilizer on account 
of the nitrates, nitrites, and decaying animal and 
vegetable matters which they contain. 

127. Ammonium Compounds of the Soil. — The 
amount of ammonium compounds in a soil is usually 
less than the amount of nitrates and nitrites. The 
sources of the ammonium compounds are : rain-water 
and the ammonia formed from the decay of the 
organic matter. Like the nitrates and" nitrites, the 
ammonium compounds are all soluble and hence can- 
not accumulate in soils which receive an average 
amount of rainfall. They are usually found in all 



Il6 SOILS AND FERTILIZERS 

surface well waters. In the soil, the ammonium com- 
pounds may be oxidized and form nitrates. Com- 
pounds as ammonium chloride or ammonium carbonate, 
if present in a soil in excessive amounts, will destroy 
vegetation in a way similar to the alkaline compounds 
in alkaline soils. 

128. Nitrogen in Rain-water and Snov/. — The 

amount of nitrogen which is annually returned to the 
soil in the form of ammonium compounds dissolved in 
rain-water and snow, is equivalent to from 2 to 3 
pounds per acre. At the Rothamsted experiment 
station the average amount for eight years was 3.37 
pounds. 43 When a soil is rich in nitrogen the gain 
from rain and snow is only a partial restoration of that 
which has been given off from the soil to the air or 
lost in the drain waters. The principal form of the 
nitrogen in rain water is ammonium carbonate which 
is present in the air to the extent of about 2 2 parts per 
million parts of air. 

129. Ratio of Nitrogen to Carbon in the Organic 
Matter of Soils. — In some soils the organic matter is 
more nitrogenous than in others. In those of the 
arid regions the humus contains from 15 to 20 per 
cent, of nitrogen, while soils from the humid regions 
contain 4 to 6 per cent.-^^ In some soils the ratio of 
nitrogen to carbon may be i to 6, while in others it 
may be i to 18 or more. That is, in some soils there 
is I part of nitrogen to 6 parts of carbon, while in 



NITROGEN COMPOUNDS OF THE SOIL II7 

others the organic matter contains i part of nitrogen 
to 18 parts of carbon. In a soil where there exists a 
wide ratio between the nitrogen and carbon, it is 
believed that the conditions for supplying crops with 
available nitrogen are unfavorable. 

130. Losses of Nitrogen from Soils. — When a soil 
rich in nitrogen is cultivated for a number of years 
exclusively to grain crops there is a loss of nitrogen 
exceeding the amount removed in the crop, caused by 
the rapid oxidation of the organic matter of the soil. 
Experiments have shown that when a soil of average 
fertility is cultivated continually to grain that for 
every 25 pounds of nitrogen removed in the crop there 
is a loss of 146 pounds from the soil due to the 
destruction of the organic matter. '7 In general, any 
system of cropping which keeps the soil continually 
under the plow, results in decreasing the nitrogen. 
When a soil is rich in nitrogen the greatest losses 
occur; when poor in nitrogen there is relatively less 
loss. There is a tendency toward the establishment 
of an equilibrium as to the nitrogen content of soils. 
When a soil rich in nitrogen is given arable culture 
the oxidation of the organic matter and the losses of 
nitrogen take place rapidly. 

131. Gain of Nitrogen in Soils. — When arable 
land is permanently covered with vegetation, there is 
a gain of nitrogen. Pasture land contains more nitro- 
gen than cultivated land of a similar character ; also 



Il8 SOILS AND FERTILIZERS 

in meadow land there is a tendency for the nitrogen 
to increase. These facts are well illustrated in the 
investigations of Lawes and Gilbert, at Rothamsted.^s 

Age of pasture. Nitrogen. 

Years. Per cent. 

Arable land 0.14 

Barn-field pasture 8 o. 151 

Apple-tree pasture 18 o. 174 

Meadow 21 0.204 

Meadow 30 0.241 

After deducting the amount of nitrogen in the manure 
added to the meadow land, the annual gain of nitrogen 
was more than 44 pounds per acre. 

Another source of gain of nitrogen is the fixation of 
the free nitrogen of the air by the growth of clover 
and other leguminous crops. If a soil is properly 
manured and cropped the amount of nitrogen may be 
increased. A rotation of wheat, clover, wheat, oats, and 
corn with manure will leave the soil at the end of the 
period of rotation in better condition as regards nitro- 
gen than at the beginning. These facts are illustrated 
in the following table :'7 

Continuous wheat culture — 

Nitrogen in soil at beginning of experiment 0.221 per cent. 

Nitrogen at end of 5 years continuous wheat cultiva- 
tion ' 0.193 " " 

Loss per annum per acre (in crop 24.5, soil 146.5) . . 171 pounds. 

Rotation of crops — 

Nitrogen in soil at beginning of rotation 0.221 per cent. 

Nitrogen at close of rotation 0.231 " " 

Gain to soil per annum per acre 61 pounds. 

Nitrogen removed in crops per annum 44 " 



NITRIFICATION II9 

It is to be regretted that in the cultivation of large 
areas of land to staple crops as wheat, corn, and cotton, 
the methods of cultivation are such as to decrease the 
nitrogen content and crop-producing power of the soil 
when this can be prevented. 

NITRIFICATION 

132. Former Views Regarding Nitrification. — 

The presence of nitrates and nitrites in soils was 
formerly accounted for by oxidation. The theory 
was held that the production of nascent nitrogen by 
the decomposition of organic matter caused a union 
between the oxygen of the air and the nitrogen of the 
organic matter. The studies of fermentation by 
Pasteur led him to believe that possibly the formation 
of nitric acid in the soil might be due to fermentation. 
It was, however, 15 years later before the French 
chemists, Schlosing and Miintz, established the fact 
that nitrification is produced by a living organism. 

133. Nitrification Caused by Micro-organisms. 

— Nitrification is the process by which nitrates 
or nitrites are produced in soils, by the workings of 
organisms. Nitrification results in changing the com- 
plex organic nitrogen of the soil to the form of nitrates 
or nitrites. It is the process by which the inert 
nitrogen of the soil is rendered available as crop food. 
The organisms which carry on the work of nitrifica- 
tion have been isolated and studied by Warington, 
and by Winogradsky. 



I20 SOILS AND FERTILIZERS 

134. Conditions Necessary for Nitrification are : 

1. Food for the nitrifying organisms. 

2. A supply of oxygen. 

3. Moisture. 

4. A favorable temperature. 

5. Absence of strong sunlight. 

6. The presence of some basic compound. 

In order to allow nitrification to proceed, all of these 
conditions must be satisfied. The process is fre- 
quently checked because some of the conditions, as 
presence of a basic compound, are unfulfilled. 

135. Food for the Nitrifying Organisms. — All 

living organisms require a supply of food and one of 
the food requirements of the nitrifying organism is a 
supply of phosphates. In the absence of phosphoric 
acid, nitrification cannot take place. The change 
which the phosphoric acid undergoes in serving as 
food for the nitrifying organism is unknown, but it 
doubtless makes the phosphoric acid more available as 
plant food. The principal organic food of the nitrify- 
ing organism is the organic matter of the soil. 
Organic matter, only when incorporated with soil, can 
serve as food for the nitrifying organism. In the pres- 
ence of a large amount of organic matter, as in a 
manure pile, nitrification does not take place. The 
process can take place only when the organic matter 
is largely diluted with soil. Under favorable condi- 




FiQ. I . Nitric Organism in Potassium Nitrite Solution. 




^^- >/ V ^ 






'^ 



X. ? 



Fig. 2. Bacillus reducing Nitrates to free Nitrogen Gas. 



PLATE I 



NITRIFICATION 121 

tions nitrifying organisms may take all of their food 
as inorganic forms; that is, nitrification may take 
place in the absence of organic matter provided the 
proper mineral food be supplied. When growth 
under such conditions takes place the organisms assim- 
ilate carbon from the combined carbon of the air, and 
produce organic carbon compounds. That is, an 
organism, working in the absence of sunlight and un- 
provided with chlorophyl, may construct organic car- 
bon compounds. '^3 The nitrification which takes place in 
the absence of nitrogenous organic matter is of too 
limited a character to supply growing crops with all 
of their available nitrogen. For general crop produc- 
tion the organic matter of the soil is the source of the 
nitrogen which undergoes the nitrification process, 
and which furnishes food for the nitrifying organisms. 

136. Oxygen Necessary for Nitrification. — The 
second requirement for nitrification is an adequate 
supply of oxygen. The nitrification organism belongs 
to that class of ferments (aerobic) which requires oxy- 
gen for existence. Oxygen is present as one of the ele- 
ments in the final product of nitrification as in calcium 
nitrate, Ca(NO )^. In the absence of oxygen the nitri- 
fication process is checked. When soils are saturated 
with water, the process cannot go on for want of oxygen. 
In well-cultivated soils, particularly clay soils, the con- 
ditions for nitrification are improved by aeration be- 
cause the supply of oxygen in the soil spaces is increased. 



122 SOILS AND FERTILIZERS 

137. Moisture Necessary for Nitrification. — Nitri- 
fication cannot take place in a soil deprived of mois- 
tnre. As in all fermentation processes, so with nitri- 
fication, moisture is necessary for the chemical changes 
to take place. In a very dry time nitrification is 
arrested for the want of water. Water is as necessary 
for the growth and development of the living organism 
which carries on the work of nitrification, as it is to 
the life of a plant of higher order. 

138. Temperatures Favorable for Nitrification. — 
The most favorable temperatures for nitrification are 
between 12° C. (54^ F.) and 2>7'' C. (99° F.). It may 
take place at as low a temperature as 3° or 4° C. 
{2)7'' and 39° F.) ; at 50° C. (122° F.) it is feeble, 
while at 55° C. (130° F.) there is no action. ^3 In 
northern latitudes nitrification is checked during the 
winter, while in southern latitudes this change takes 
place during the entire year. Crops which re- 
quire their nitrogen early in the growing season are 
frequently placed at a disadvantage because there is less 
available nitrogen in the soil at that time than later. 

139. Strong Sunlight Checks Nitrification. — Nitri- 
fication cannot take place in strong sunlight ; it pre- 
vents the action of all organisms of this class. In 
fallow land there is no nitrification at the surface but 
immediately below where the surface soil excludes the 
sunlight, it is most active. In a cornfield it is more 
active than in a compacted fallow field. 



NITRIFICATION 123 

140. Base-forming Elements Essential for Nitrifi- 
cation. — The presence of some base-forming element to 
combine with the nitric acid produced is a necessary 
condition for nitrification, and for this purpose calcium 
carbonate is particularly valuable. The absence of 
basic materials is one of the frequent causes of non- 
nitrification. In acid soils, the process is checked for 
the want of proper basic material. The organisms 
which carry on the work cannot exist in a strong acid 
or alkaline solution, consequently in strong acid or 
alkaline soils the ordinary process cannot take place. '^ 

141. Nitrous Acid Organisms. — There are at least 
two nitrifying organisms in the soil : one produces 
nitrates and the other nitrites or nitrous acid. It is 
believed that the process takes place in two stages, the 
first being performed by the nitrous organism, and the 
process completed by the nitric organism. Warington 
says that "both organisms are present in the soil in 
enormous numbers, — and the action of the two organ- 
isms proceeds together, as the conditions are favorable 
to both." 

142. Ammonia-producing Organisms. — There are 
also present in the soil organisms which have the 
power of producing ammonia from proteid bodies. 
The ammonium compounds produced are acted upon 
by the nitrifying organisms and readily undergo 
nitrification, ^s 

143. Denitrification is just the reverse of the nitri- 



124 SOILS AND FERTILIZERS 

fication process, and is the result of the workings of a 
class of organisms which feed upon the nitrates form- 
ing free nitrogen which is liberated as a gas. One of 
the conditions for denitrification is absence of air, as 
the organism belongs to the anaerobic class. Denitri- 
fication readily takes place in soils saturated with 
water, and where the soil is compacted so that air is 
practically excluded. "^^ 

144. Number and Kinds of Organisms in Soils. — 

In addition to the micro-organisms which carry on the 
work of nitrification, denitrification, and ammonifica- 
tion, there are a great many others, some of which are 
beneficial while others are injurious to crop growth. 
It has been estimated that in a gram of an average 
sample of soil there are from 60,000 to 500,000 bene- 
ficial and injurious micro-organisms. ^^ There are pro- 
duced from many crop residues, by injurious ferments, 
chemical products which may be destructive to crop 
growth. Flax straw for example when it decays in 
the soil forms products which are destructive to a suc- 
ceeding flax crop. 

A moist soil, rich in organic matter, and containing 
various salts, may form the medium for the propaga- 
tion of all classes of organisms. Sewage-sick soils, 
clover-sick soils, and flax-diseased lands are all the re- 
sults of bacterial diseases. Many of the organisms 
which are the cause of such diseases as typhoid fever, 
cholera, and diphtheria, may propagate and develop 



NITRIFICATION I25 

in a moist soil under certain conditions, and then find 
their way through drain waters into surface wells, and 
cause the spreading of these diseases. 

145. Products Formed by Soil Organisms. — In 

considering the part which micro-organisms take in 
plant growth, as well as in all similar processes, there 
are two phases to be considered : (i) the action of the or- 
ganism itself, and (2) the chemical action of the product 
of the organism. In the case of nitrification, the 
action of the organism brings about a change in the 
composition of the organic matter, producing nitric 
acid which is merely a product formed as a result of 
the action of the organism. The nitric acid then acts 
upon the soil producing nitrates. In the case of soils 
rich in organic matter, the fermentation changes 
which take place during humification result in the 
production of acid products. This is simply the 
result of the action of the ferments. The acids then 
act upon the soil bases and produce humates or organic 
salts. In many fermentation changes there is first 
the production of some chemical compound, and then 
the action of this compound upon other bodies. In 
rendering plant food available, as in nitrification and 
humification, it is the final product, and not the first 
product of the organism, which is of value. 

146. Inocculating Soils with Organisms. — Ingrow- 
ing leguminous crops on soils where they have never 
before been produced, it has been proposed to supply 



126 SOILS AND FERTILIZERS 

the essential organisms which assist the crops to 
obtain their nitrogen. For example, if clover is 
grown on new land, the soil is liable to be deficient in 
the organisms which assist in the assimilation of 
nitrogen and which are present in the root nodules of 
the plant. If these organisms are supplied, better 
conditions for growth exist. The extent to which it 
is necessary to inoculate soils with organisms for the 
assimilation of nitrogen, has not yet been determined 
by actual field experiments. 

147. Loss of Nitrogen by Fallowing Rich Lands. 
— Summer fallowing creates conditions favorable to 
nitrification. A fallow is beneficial to a succeeding 
crop because of the nitrogen which is rendered avail- 
able. If a soil is rich in nitrogen and lime, summer 
fallowing causes the production of more nitrates than 
can be retained in the soil. The crop utilizes only a 
part of the nitrogen rendered available, the rest being 
lost by drainage, ammonification, and denitrification. 
Hence the available nitrogen is increased while the 
total nitrogen is greatly decreased. '^ 

Soil before Soil after 

fallowing. fallowing. 

Total nitrogen o. 154 o. 142 

Soluble nitrogen 0.002 0.004 

The gain of 0.002 per cent, of soluble nitrogen was 
accompanied by a loss of 0.012 per cent, of total 
nitrogen. For every pound of available nitrogen 
there was a loss of 6 pounds. 



NITRIFICATION I27 

148. Deep and Shallow Plowing and Nitrification. 

— In a rich prairie soil nitrification goes on very 
rapidly. This is one reason why shallow plowing on 
new breaking gives better results than deep plowing. 
Deep plowing at first causes nitrification to take place 
to such an extent that the crop is overstimulated in 
growth. Deep plowing and thorough cultivation aid 
nitrification. The longer a soil has been cultivated, 
the deeper and more thorough must be the cultivation. 

149. Spring and Fall Plowing, and Nitrification. 

— Early fall plowing leaves more available nitrogen 
at the disposal of the crop than late fall plowing. 
Nitrification takes place only near the surface. Hence 
when late spring plowing is practiced there is brought 
to the surface raw nitrogen, while the available 
nitrogen has been plowed under, and is beyond the 
reach of the young plants when they require the most 
help in obtaining food. The various methods of 
cultivation as deep and shallow plowing, spring 
and fall plowing, and surface cultivation have as much 
influence upon the available nitrogen supply of crops 
as upon the water supply. The saying that cultiva- 
tion makes plant food available is particularly true of 
the element nitrogen, the supply of which is capable 
of being increased or decreased to a greater extent 
than that of any other element. 



NITROGENOUS MANURES 

150. Sources of Nitrogenous Manures. — The 

materials used for enriching soils with nitrogen, to 
promote crop growth, may be divided into three 
classes: (i) organic nitrogenous manures, (2) nitrates, 
and (3) ammonium salts. Each of these classes has a 
different value as plant food. In fact there are 
marked differences in fertilizer value between mate- 
rials belonging to the same class. The nitrogenous 
organic materials used for fertilizing purposes are : 
dried blood, tankage, meat scraps and flesh meal, fish 
offal, cottonseed meal, and leguminous crops as clover 
and peas. The nitrogen in these substances is princi- 
pally in the form of protein. When peat and muck 
are properly used they may also be classed among the 
nitrogenous manures. 

151. Dried Blood. — This is obtained by drying the 
blood and debris from slaughter-houses. Frequently 
small amounts of salt and slaked lime are mixed with 
the blood. It is richest in nitrogen of any of the 
organic manures. When thoroughly dry it may con- 
tain 14 per cent, of nitrogen. As usually sold, it con- 
tains from 10 to 20 per cent, of water, and has a 
nitrogen content of from 9 to 13. Dried blood 
contains only small amounts of other fertilizer ele- 
ments. It is strictly a nitrogenous fertilizer, readily 
yielding to the action of micro-organisms and to 



NITROGENOUS MANURES 1 29 

nitrification ; on account of its fermentable nature, it 
is a quick-acting fertilizer, and is one of the most 
valuable of the organic materials used as manure. 
Dried blood may be applied as a top dressing on grass 
land. It gives the best returns when used on an 
impoverished soil to aid crops in the early stages of 
growth, before the inert nitrogen of the soil becomes 
available. It is also an excellent form of fertil- 
izer to use on many garden crops, but it should not be 
placed in direct contact with seeds, as it will cause 
rotting, nor should it be used in too large amounts. 
Three hundred pounds per acre is as much as should 
be applied at one time. When too nuich is used losses 
of nitrog^en mav occur bv leaching- and bv denitrifica- 
tion. It is best applied directh- to the soil, as a top 
dressing in the case of grass, or near the seeds of 
garden crops, and not mixed with unslaked lime or 
wood ashes, but each should be used separately. As 
all plants take up their nitrogen early in their growth, 
nitrogenous fertilizers as blood should be applied be- 
fore seeding or soon after. An application of dried 
blood to partially matured garden crops will cause a 
prolonged growth and very late maturity. 

Storer gives the following directions for preserving 
any dried blood produced upon farnus.^' " The blood 
is thoroughly mixed in a shallow box wnth 4 or 5 
times its weight of slaked lime. The mixture is cov- 
ered with a thin layer of lime and left to dry out. It 



130 SOIIvS AND FERTILIZERS 

will keep if stored in a cool place, and may be applied 
directly to the land or added to a compost heap." 

The price per pound of nitrogen in the form of 
dried blood can be determined from the cost and the 
analysis of the material. A sample containing 9 per 
cent, of nitrogen and selling for $20 per ton is equiva- 
lent to 1 1. 1 1 cents per pound for the nitrogen (2000 X 
0.09 = 180. $20.00 H- 180 = 1 1. 1 1 cents). 

152. Tankage is composed of miscellaneous refuse 
matter as bones, trimmings of hides, hair, horns, hoofs, 
and some blood. The fat and gelatin are, as a rule, 
first removed by subjecting the material to superheated 
steam. This miscellaneous refuse, after drying, is 
ground and sometimes mixed with a little slaked lime 
to prevent rapid fermentation. 

Tankage contains less nitrogen but more phosphoric 
acid than dried blood. Owing to its miscellaneous 
nature, it is quite variable in composition, as the fol- 
lowing analyses of tankage from the same abattoir at 
different times show.'^ 

First j'ear. Second year. T,hird year. 

Moisture 10.5 9.8 10.9 

Nitrogen 5.7 7.6 6.4 

Phosphoric acid 12.2 10.6 11.7 

As a general rule, tankage contains from 5 to 8 per 
cent, of nitrogen and from 6 to 14 per cent, of phos- 
phoric acid. It is much slower in its action than 
dried blood, and supplies the crop with both nitrogen 
and phosphoric acid. Tankage is a valuable form of 



NITROGENOUS MANURES 131 

fertilizer to use for garden purposes. It may also be 
used as a top dressing on grass lands, and may be 
spread broadcast on grain lands. It is best to apply 
the tankage, when possible, a few days prior to seed- 
ing, and it should not come in contact with seeds. 
Two hundred and fifty pounds per acre is a safe dress- 
ing, and when there is sufficient rain to ferment the 
tankage, 400 pounds per acre may be used. A dressing 
of 800 pounds in a dry season would be destructive to 
vegetation. On impoverished soil more may be used 
than on soils which are for various reasons out of 
condition. The cost of the nitrogen, as tankage, may 
be determined from the composition and selling price. 
If tankage containing 7 per cent, of nitrogen and 12 
per cent, of phosphoric acid is selling for $22 per ton, 
w^hat is the cost of the nitrogen per pound ? The 
market value of phosphoric acid, in the form of bones, 
should first be ascertained. Suppose that bone phos- 
phoric acid is selling for 4 cents per pound. The 
phosphoric acid in the ton of tankage would then be 
worth $9.60, making the nitrogen cost $12.40. The 
140 pounds of nitrogen in the ton of fertilizer would 
then be worth $12.40, or 8.8 cents per pound. In 
eastern markets the price of tankage is usually much 
higher than near the large packing houses of the west. 

153. Flesh Meal. — The flesh refuse from slaugh- 
ter-houses is sometimes kept separate from the tank- 
age and sold as flesh meal, the fat and gelatin being 



132 SOILS AND FERTILIZERS 

first removed and used for the manufacture of glue and 
soap. Flesh meal is variable in composition and may 
be very slow in decomposing. It contains from 4 to 
8 per cent, or more of nitrogen with an appreciable 
amount of phosphoric acid. Occasionally it is used 
for feeding poultry and hogs, and cattle to a limited 
extent. When thus used the fertilizer value of the 
dung is nearly equivalent to the original value of the 
meal. 

154. Fish Scrap. — The flesh of fish is very rich in 
nitrogen. ^^ The offal parts, as heads, fins, tails, and in- 
testines, are dried and prepared as a fertilizer. jMany 
species of fish which are not edible are caught in large 
numbers to be used for this purpose. In sea-coast 
regions fish fertilizer is one of the cheapest and best of 
the nitrogenous manures. It is richer in nitrogen 
than tankage or flesh meal, and in many cases equal 
to dried blood. It readily undergoes nitrification and 
is a quick-acting fertilizer. 

155. Seed Residues. — ]\Iany seeds, as cottonseed 
and flaxseed, are exceedingly rich in nitrogen. When 
the oil has been removed, the flaxseed and cottonseed 
cake are proportionally richer in nitrogen than the 
original seed. This cake is usually sold as cattle 
food, but occasionally used as fertilizer. Cotton- 
seed cake contains from 6 to 7 per cent, of nitro- 
gen, and compares fairly well in nitrogen content with 
animal bodies. Cottonseed cake or meal is not so 



NITROGENOUS MANURES I 33 

quick-acting a fertilizer as dried blood, but when used 
in southern latitudes a little time before seeding, the 
nitrogen becomes available for crop purposes. Cot- 
tonseed or linseed meal containing a high per cent, of 
oil is much slower in decomposing than that which 
contains but little oil. It is generally considered bet- 
ter economy to feed the cake to stock and use the 
manure than to apply the cake directly to the land. 
Of late years cottonseed-meal has been so reduced in 
price that its use as a fertilizer has been admissible. 

A ton of cottonseed-meal costing $20 and contain- 
ing 2 per cent, of phosphoric acid and 7 per cent, of 
nitrogen would be equivalent to buying the nitrogen 
at 1 3. 1 cents per pound, which is frequently cheaper 
than purchasing some other nitrogen fertilizer. 

156. Leather, Wool Waste and Hair are rich in 
nitrogen, but on account of their slow rate of decom- 
posing are unsuitable for fertilizer purposes. When 
present in fertilizers they give poor field results. 

157. Solubility of Organic Nitrogenous Mate- 
rials. — The method employed to detect, in fertilizers, 
the presence of inert forms of nitrogen as leather, is to 
digest the material in prepared pepsin solution.^5 
Substances like dried blood are nearly all soluble in 
the pepsin, while leather and inert forms are only par- 
tially so. The solubility of organic nitrogen in pep- 
sin solution determines, to a great extent, the value of 
the material as a fertilizer. 5° 



134 SOILS AND FERTILIZERS 

Soluble in prepared 

pepsin solution. 
Per cent, of nitrogen. 

Dried blood 94.2 

Ground dried fish 75.7 

Tankage 73.6 

Cottonseed meal 86.4 

Hoof and horn meal 30.0 

Leather 16.7 

158. Peat and Muck. — Many samples of peat and 
mnck are quite rich in nitrogen. The nitrogen is, 
however, in a very insokible form, and is with diffi- 
culty nitrified. When mixed with stable manure, 
particularly liquid manure, with the addition of a lit- 
tle lime, fermentation may be induced, and a valuable 
manure produced. Muck or peat should be dried and 
sun-cured, and then used as an absorbent m stables. 
Peat differs from muck in being fibrous. If the muck 
gives an acid reaction, lime (not quicklime) should be 
used with it in the stable, as directed under farm 
manures. When easily obtained muck is one of the 
cheapest forms of nitrogen. 



Composition of Muck Samp[,es.*^ 



Nitrogen. 
Per cent. 



Marshy place, producing hay 2.21 

Marshy place, dry in late summer 2.01 

Old lake bottom 1.81 

159. Leguminous Crops as Nitrogenous Manures. 

— The frequent use of leguminous crops for manurial 
purposes is the cheapest way of obtaining nitrogen. 
When the crop is not removed from the land but is 



NITROGENOUS MANURES I 35 

plowed under while green, the practice is called green 
manuring. This does not enrich the land with any 
mineral material- but results in changing to humate 
forms inert plant food. Green manuring should take 
the place of bare fallow, as its effects are in many 
respects more beneficial. With green manuring, 
nitrogen is added to the soil while with bare fallow 
there is a loss of nitrogen. Leguminous crops, as 
clover, peas, crimson clover, and cow peas, should be 
made to serve as the main source of the nitroeren for 
crop production. 

160. Sodium Nitrate. — The nitric nitrogen most 
frequently met with in commercial forms is sodium 
nitrate, commonly known as Chili saltpeter. It is a 
natural deposit found extensively in Chili, Peru, and 
the United States of Colombia. Various theories have 
been proposed to account for these deposits, but it is 
difficult to determine just how they have been formed. '° 
Their value to agriculture may be estimated from the 
fact that there are annually used in the United States 
about 100,000 tons, and in Europe about 700,000 tons. 
The commercial value of nitrogfen in fertilizers is ree- 
ulated by the price of sodium nitrate which, when pure, 
contains 16.49 P^^ cent, of nitrogen. Commercial 
sodium nitrate is from 95 to 97 per cent. pure. 
An ordinary sample contains about 16 per cent, 
of nitrogen and costs from $50 to $60 per ton, making 
the nitrogen worth from 15 to 18 cents per pound. 



136 SOILS AND FERTILIZERS 

Sodium nitrate is tlie most active of all the nitrogenous 
manures. It is soluble and does not have to undergo 
the nitrification process before being utilized by crops. 
On account of its extreme solubility it should be ap- 
plied sparingly, for it cannot be retained in the soil. 
As a top dressing on grass, it will respond by impart- 
ing a rich green color. It may be used at the rate of 
250 pounds per acre, but a much lighter application 
will generally be found tnore economical. Sodimn 
nitrate may contain traces of sodium perchlorate, 
which is destructi\-e to \egetation, if the fertilizer is 
used in excess.^' Sodium nitrate, in small amounts, 
is the fertilizer most frequently resorted to when the 
forcing of crops is desired as in early market garden- 
ing. Its use for fertilizing horticultural crops has be- 
come equally as extensi\e as for general farm crops. 
Excessive amounts of sodium nitrate may produce in- 
jurious results. It stimulates a rank growth of dark 
green foliage, and retards the maturity of plants, but 
when properly used it is one of the most valuable of 
the nitrogenous fertilizers. 

161. Ammonium Salts. — Ammonium sulphate is 
obtained as a by-product in the manufacture of illumi- 
nating S^as and is extensivelv sold as a fertilizer. It 
usually contains about 20 per cent, of nitrogen, equiv- 
alent to 95 per cent, of ammonium sulphate, the re- 
maining 5 per cent, being moisture and impurities. 
Ammonium sulphate is not generally considered the 



NITROGENOUS MANURES 137 

equivalent of sodium nitrate. It is, however, a valua- 
ble form of nitrogen. The statements made regarding 
the use of sodium nitrate apply equally well to the use 
of ammonium sulphate. Ammonium chloride and 
ammonium carbonate are not suitable for fertilizers on 
account of their destructive action upon vegetation. 

162. Nitrogen and Ammonia Equivalent of Fer- 
tilizers. — Nitrogenous fertilizers are sometimes 
represented as containing a certain amount of ammo- 
nia instead of nitrogen ; this is so that a higher per- 
centage may be made to appear. Fourteen-seven- 
teenths of ammonia is nitrogen, and if a fertilizer is 
said to contain 2.25 per cent, ammonia, it is equiva- 
lent to 1.85 per cent, of nitrogen. 

163. Purchasing Nitrogenous Manures. — In pur- 
chasing nitrogenous manure, the special purpose for 
which it is to be used should always be considered. 
Under some conditions, as forcing a crop on an im- 
poverished soil, sodium nitrate is desirable. Under 
other conditions tankage, cottonseed cake, or some 
other form of nitrogen may be made to answer the 
purpose. There is annually expended in purchasing 
nitrogenous fertilizers a large amount of money which 
could be expended more economically, if the science 
of fertilizing were given a more careful study. 



CHAPTER V 



FIXATION 

164. Fixation, a Chemical Change. — When a fertil- 
izer is applied to a soil chemical changes take place 
between the soil and the fertilizer. There is a general 
tendency for the soluble matter of fertilizers to undergo 
Chemical changes and become insoluble. This pro- 
cess is known as fixation. If a solution of potassium 
chloride be percolated through a column of clay, the 
filtrate will contain scarcely a trace of potassium chlo- 
ride, but instead calcium and other chlorides. In its 
action upon the soil, the potassium chloride has un- 
dergone a chemical change, the element potassium 
being replaced by the element calcium. An ex- 
change has taken place between the two bases. 

165. Fixation Due to Zeolites. — It has been shown 
by experiments, particularly by Way and Voechler, 
that fixation is due mainly to the zeolitic silicates.^^ 
Sandy soils containing but little clay have only a fee- 
ble power of fixation. Clay soils when digested with 
hydrochloric acid to remove the zeolitic silicates, lose 
their power of fixation. The fixation of potassium 
chloride and the liberation of calcium chloride may be 
illustrated bv the following^ reaction : 



FIXATION 139 

^^^^ K.(SiO,),.H,0-2HCl =p4o, [x(SiO,)..H,0 + CaCl^. 
etc. J etc. J 

166. Humus May Cause Fixation. — Other com- 
pounds of the soil as humus and calcium carbonate 
may also take an important part in fixation. In the 
case of humus a union takes place between the basic 
material and the organic matter of the soil. 

167. Soils Possess Different Powers of Fixation. — 
All soils do not possess the power of fixation to the 
same extent. Heavy clays have the greatest fixative 
power while sandy soils have the least. Experiments 
have shown that in the first nine inches of soil from 
2,000 to 8,000 pounds per acre of potash and phos- 
phoric acid may undergo fixation." Hence it is that 
a fertilizer, after being applied to a soil, may be en- 
tirely changed in composition, so that the plant feeds 
on the chemical compounds formed, rather than on the 
original fertilizer. 

168. Nitrates Cannot Undergo Fixation. — Nitro- 
gen in the form of nitrates or nitrites cannot undergo 
fixation. This is because all of the ordinary forms of 
nitrates are soluble. If potassium nitrate be added to 
a soil, calcium nitrate will doubtless be obtained as the 
soluble compound. The potassium undergoes fixa- 
tion, but the nitrate radical does not. Chlorides are 
likewise incapable of undergoing fixation. 

169. Fixation May Make Plant Food Less Availa- 
ble. — If a liberal dressing of phosphate fertilizer be 



140 SOILS AND FERTILIZERS 

applied to a heavy clay soil, the phosphoric acid which 
is not utilized the first year or two may undergo fixa- 
tion to such an extent as to become unavailable as 
plant food. It is not desirable to apply heavy dress- 
ings of fertilizers at long intervals because of fixation. 
It is always best to make lighter applications and more 
frequently. 

170. Fixation, a Desirable Property of Soils. — If it 
were not for the process of fixation, soils in regions of 
heavy rains would soon become sterile. On account 
of the plant food being rendered insoluble, it is re- 
tained in the soil. The plant food which undergoes 
fixation is, as a rule, in an available condition, unless 
the soil be one of unusual composition. The fixation 
of fertilizers regulates the supply of crop food. Many 
fertilizers, if they did not undergo this process, would 
be injurious to crops. There would be an abnormal 
amount of soluble alkaline or acid compounds which 
would be destructive. The process of fixation first 
taking place removes, to a great extent, the water-solu- 
ble salts, particularly when the reaction is one of 
union rather than replacement. Then the plant is 
free to render soluble its own plant food in quantities 
and at times desired. 

Farm manures and commercial fertilizers alike un- 
dergo the process of fixation and, in studying fertilizers, 
their action upon the soil and the products of fixation 
are matters of prime importance. 



CHAPTER VI 

FARM MANURE 

171. Variable Composition of Farm Manures. — 

The term ' farm manure' does not designate a prod- 
uct of definite composition. Manure is the most 
variable in chemical composition of any of the mate- 
rials produced on the farm. It may contain a large 
amount of straw, in which case it is called coarse ma- 
nure ; or it may contain only the solid excrements and 
a little straw, the liquid excrements being lost by 
leaching ; then again it may consist of the droppings 
of poorly fed animals, or of the mixed excrements of 
different classes of well-fed animals. 

The term ' stable manure' has been proposed for 
that product which contains all of the solid and liquid 
excrements with the necessary absorbent, before any 
losses have been sustained. '^ The term ' barnyard 
manure' is restricted to that material which ac- 
cumulates around some barns and farm yards, and is 
exposed to leaching rains and the drying action of the 
sun. 

172. Average Composition of Manures. — The solid 
excrements of animals contain from 60 to 85 per cent, 
of water ; when mixed with straw, and the liquid 
excrements are retained, the mixed manure con- 



142 



SOILS AND FERTILIZERS 



tains about 75 per cent, of water. The nitrogen va- 
ries from 0.4 to 0.9 per cent, according to the nature of 
the food and the extent to which other factors have af- 
fected the composition. In general, animals consu- 
ming liberal amounts of coarse fodders produce manure 




AVater 



Fig. 25. Manure after six 
■ months' exposure. 



Fig. 24. Average composition of 

fresh manure. 

I . Nitrogen. 2. Phosphoric acid. 

3. Potash. 

with a higher per cent, of potash than of phosphoric 
acid. This is because the potash in the food exceeds 
the phosphoric acid. The average composition of 
mixed stable manure is about as follows : 



Average. 
Per cent. 



Nitrogen 0.50 

Phosphoric acid 0.35 

Potash 0.50 



Range. 
Per cent. 

0.4 to 0.8 

0.2 to 0.5 

0.3 to 0.9 



In calculating the amount of fertility in manures, it 
is more satisfactory to compute the value from the food 
consumed and the care which the manure has received, 
than to use figures expressing average composition. 



FARM MANURE 143 

173. Factors which Influence the Composition and 
Value of Manure. — 

I. Kind and amount of absorbents used. 

II. Kind and amount of food consumed. 

III. Age and kind of animals. 

IV. Methods employed in collecting, preser\'ing 
and utilizing the manure. 

Any one of the above, as well as many minor factors, 
may influence the composition and value of stable 
manure. 

174. Absorbents. — The most universal absorbent 
is straw. Wheat straw and barley straw have about 
the same manurial value. Oat straw, however, is 
more valuable. The average composition of straw 
and other absorbents is as follows : 

straw. Leaves. Peat. Sawdust. 

Per cent. Per cent. Per cent. Per cent. 

Nitrogen 0.40 0.6 i.o o.i 

Phosphoric acid 0.36 0.3 •. 0.2 

Potash 0.80 0.3 .. 0.4 

When a large amount of straw is used the per cent, 
of nitrogen and phosphoric acid is decreased, while the 
per cent, of potash is slightly increased. Sawdust 
and leaves both make the manure more dilute. Dry 
peat makes the manure richer in nitrogen. The ab- 
sorbent powers of these different materials are about as 
follows :'3 



144 SOILS AND FERTILIZERS 

Per cent, of 
water absorbed. 

Fine cut straw 30.0 

Coarse uncut straw 18.0 

Peat 60.0 

Sawdust 45.0 

The proportion of absorbents in niannre ranges from 
^ fifth to a third of the total weight of the manure. 

175. Use of Peat and Muck as Absorbents. — On 
account of the high per cent, of nitrogen in peat and 
the power which it possesses when dry of absorbing 
water, it is a valuable material to use as an absorbent 
in stables. As previously explained, peat is slow of 
decomposition, but when mixed with the liquid ma- 
nure it readily yields to fermentation, particularly if a 
little land plaster or marl be used in the stable along 
with the peat. Peat has a high absorptive power for 
gases as well as liquids, and when used stables are ren- 
dered particularly free from foul odors. 

RELATION OF FOOD CONSUMED TO MANURE PRODUCED 

176. Bulky and Concentrated Foods. — The more 
concentrated and digestible the food consumed, the 
more valuable is the manure. Coarse bulky fodders 
always give a large amount of a poor quality of ma- 
nure. For example, the manure from animals fed on 
timothy hay and that from animals fed on clover hay 
and grain, show a wide difference in composition. 
The dry matter of timothy hay is about 55 per cent, 
digestible. From a ton of timothy ha}' there will be 



FOOD CONSUMED TO MANURE PRODUCED 145 

about 792 pounds of dry matter in the manure. The 
nitrogen, phosphoric acid, and potash in the food con- 
sumed are nearly all returned in the manure, except 
under those conditions which will be noted. The 
manure from a ton of mixed feed, as clover and bran, 
will be smaller in amount but more concentrated than 
that produced from timothy. In a ton of timothy and 
in a ton of mixed feed (1500 lbs. clover, 500 lbs. bran) 
there are present : 

Timothy. Mixed feed. 

I,bs. Lbs. 

Nitrogen 25.0 40.0 

Phosphoric acid 9.0 24.0 

Potash 40.0 30.0 

The nitrogen, phosphoric acid, and potash in these 
two rations are retained in the animal bodies in dis- 
similar amounts ; that is, 10 per cent, more of these 
elements are retained from the more liberal ration, due 
to more favorable conditions for growth. Making al- 
lowance for this fact there will be present in the ma- 
nure from the mixed feed one-half more nitrogen, and 
two and one-half times as much phosphoric acid, as 
in the manure from the timothy hay, which, free 
from bedding, contains about 792 pounds of indigesti- 
ble matter while that from the mixed feed con^ 
tains 760 pounds, the mixed ration being more digesti- 
ble. If both manures contain the same amount of ab- 
sorbents, the manure from the ton of mixed clover 
and bran will weigh slightly less, but contain more 
fertility than that from the timothy hay. 



146 SOILS AND FERTILIZERS 

The value of the manure can be approxhnately de- 
termined from the composition of the food consumed. 
Only a small amount of the nitrogen in the food is re- 
tained in the body. The larger portion is used for re- 
pair purposes. The nitrogen of the tissues which 
have been renewed is voided as urea in the liquid ex- 
crements. Some of the nitrogenous compounds of the 
food are utilized for the production of fat, in which 
case the nitrogen is voided in the excrements. The 
fact that but little of the nitrogen of the food, under 
most conditions, is retained in the body may be ob- 
served from the figures of Lawes and Gilbert relating 
to the composition of the flesh added to animals while 
undergoing the fattening process. ^^^ 

Increase during Fattening. 

Dry Nitrogenous 

Water. matter. Fat. matter. Ash. 

Ox 24.6 75.4 66.2 7.69 1.47 

Sheep 20.1 79.9 70,4 7.13 2.36 

Pigs 22.0 78.0 71.5 6.44 0.06 

The results of numerous digestion experiments 
show that when the food undergoes digestion from 5 
to 15 per cent, of the nitrogen is, as a rule, retained in 
the body. The nitrogen of the food is utilized largely 
to replace that which has been required for vital func- 
tions. The nitrogen of the food enters the body, un- 
dergoes digestion changes, is utilized for some vital 
function, and is then voided in the excrements. 

The digestion of the food has been compared to the 



FOOD CONSUMED TO MANURE PRODUCED 147 

combustion of fuel : the undigested products of the 
solid excrements represent the ashes, and the urine 
represents the volatile products. When wood is 
burned the nitrogen is converted into volatile products. 
When food is digested and utilized by the body the di- 
gestible nitrogen is mainly converted into urea, while 
the undigestible nitrogen is voided in the dung. 

177. Composition of Solid and Liquid Excrements 
Compared. — In composition the liquid excrements 
differ from the solids in having a much larger amount 
of nitrogen and less phosphoric acid.^s 



Water. 

Solids. lyiquids. 

Per cent. Per cent. 


Nitro 
Solids. 
Percent, 


gen. 
Liquids. 
, Percent. 


Phosphoric acid. 
Solids. Liquids. 
Per cent. Percent. 


Potash. 

Solids. 

Per cent. 


Cows . . 76 


89 


0.50 


1.20 


0.35 




0.30 


Horses. 84 


92 


0.30 


0.86 


0.25 




p. ID 


Pigs... 80 


97.0 


0.60 


0.80 


0.45 


0.12 


0.50 


Sheep . 58 


86.5 


0.75 


1.40 


0.60 


0.05 


0.30 



The nitrogen of the food consumed influences the 
amount of water in the manure. As a rule, a highly 
concentrated nitrogenous ration, produces a higher per 
cent, of water in the manure than a well-balanced 
ration. There is but little phosphoric acid in the 
liquid excrements of horses and cows, while the urine 
of sheep and swine contains appreciable amounts of 
this element. 

The liquid manure is more constant both in compo- 
sition and amount than the solid excrements. This 
fact may be observed from the following table, which 
gives the composition of the solid and liquid excre- 



148 



SOII.S AND FERTILIZERS 



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FOOD CONSUMED TO MANURE PRODUCED 149 

ments from hogs when fed on different amounts of 
grain. 56 

The amount of waste matter in the urine is nearly 
the same whether an animal be gaining or losing in 
flesh, consequently the urine is more constant in both 
composition and quantity than the solid excrements. 

The amount and composition of the solid excre- 
ments vary with the amount and kind of food con- 
sumed. If the food is indigestible the solid excrements 
contain a larger part of the nitrogen as indigestible 
protein. When the body is properly supplied with 
food for all purposes, normal conditions exist, and the 
amount of nitrogen voided in the liquid and solid ex- 
crements is no more than that supplied in the food 
consumed. 

178. Manurial Value of Foods. — The manurial 
value of fodder is determined by the amount of nitro- 
gen, phosphoric acid, and potash present in the material. 
Timothy hay, for example, has a manurial value of 
$5.30 per ton, which means that if the nitrogen, phos- 
phoric acid, and potash in the timothy hay were pur- 
chased in commercial forms they would cost $5.30. 
Lawes and Gilbert estimate that 80 per cent, of the 
fertility in fodders is, as a rule, returned in the ma- 
nure. 

In the following table are given the pounds of 
nitrogen, phosphoric acid, and potash per ton of ma- 
terial :57 



150 SOILS AND FERTILIZERS 

Nitrogen. Phosphoric acid. Potash. 

I/bs. Lbs. Lbs. 

Timothy hay 25 9 40 

Clover hay 45 14 30 

Wheat straw 11 4 12 

Oat straw 12 4 18 

Wheat 45 20 12 

Oats 33 16 II 

Barley 40 18 11 

Rye 42 20 13 

Flax 87 32 14 

Corn 32 14 8 

Wheat Shorts 48 31 20 

Wheat Bran 54 52 30 

Oil meal 100 35 25 

Cottonseed meal 130 35 56 

Milk i<^ 3 3 

Chee.se 90 23 5 

Live cattle 53 37 3 

Potatoes 7 3 II 

Butter I I I 

Live pigs 40 17 3 

179. Commercial Value of Manures. — When the 
value of farm manure is calculated on the same basis 
as that of commercial fertilizers it will be found that 
stable manure is worth from $2 to $3.50 per ton. The 
value of the increased crop resulting from the use of 
manure will vary with conditions. It is sometimes 
stated that the phosphoric acid and potash in stable 
manures is not as soluble as that in commercial fer- 
tilizers, and consequently it is worth less. While not 
so soluble in the form of manure, it frequently hap- 



AGE AND KIND OF ANIMAL 15I 

pens that the phosphoric acid and potash in the com- 
mercial fertilizers become, through fixation processes, 
less soluble when mixed with the soil than the same 
elements in stable manure. 

Stable manure is valuable not only for the fertility 
contained but also because it makes the inert plant 
food of the soil more available and exercises such a 
favorable influence on the water supply of crops; hence 
it is justifiable to assign the same value to the ele- 
ments in well-prepared farm manures as to those in 
commercial fertilizers. 

If well-prepared stable manure is not worth $2.50 
per ton, then too much, accordingly, is paid for com- 
mercial forms of plant food. 

INFLUENCE OF AGE AND KIND OF ANIMAL 

180. Manure from Young and Mature Animals. — 

The manure from older animals is more valuable than 
that from young animals, even wdien fed the same 
kind of food. This is because more of the phosphoric 
acid and nitrogenous matters are retained in the body 
of a young animal. It is not so much a difference in 
digestive power as a difference in retentive power. In 
older animals the proportion of new nitrogenous tissue 
produced is much less than in young animals, and 
more of the nitrogen of the food is used for repair pur- 
poses and subsequently voided in the manure, while 
with younger animals more of the nitrogen of the food 
is retained for the construction of new muscular tissue. 



152 SOILS AND FERTILIZERS 

The difference in composition between the manure of 
old and of young animals is not, however, so great as 
might appear. 

When an animal is neither gaining nor losing in 
flesh, and is not producing milk, an equilibrium is 
established between the nitrogen in the food supply 
and the nitrogen in the manure. Under such condi- 
tions practically all of the nitrogen of the food is re- 
turned in the manure. ^^ 

i8i. Cow Manure. — A milch cow when fed a bal- 
anced ration, will make from 60 to 70 pounds of solid 
and liquid manure a day, of which 20 to 30 pounds are 
liquid excrements. The solid excrements contain 
about 6 pounds of dry matter. When a cow is fed 
clover hay, corn fodder, and grain, about half of the 
nitrogen of the food is in the urine, about one-fourth 
in the milk, and the remainder in the solid excre- 
ments. Hence, if the solid excrements only are col- 
lected, but a quarter of the nitrogen of the food is ob- 
tained, while if both solids and liquids are utilized 
three-quarters of the nitrogen is secured. Cow manure 
is extremely variable in composition, and is the most 
bulky of any manure produced by domestic animals. 
A well-fed cow will produce about 80 lbs. of manure 
per day, including absorbents. 

182. Horse Manure. — Horse manure contains less 
water than cow manure, and is of a more fibrous 
nature, doubtless due to the horse possessing less 



AGE AND KIND OF ANIMAL I53 

power for digesting cellulose materials. Horse ma- 
nure readily ferments and gives off ammonia products. 
When the manure becomes dry, fire-fanging results, 
due to rapid fermentation followed by the growth of 
fungus bodies. Horse manure is generally considered 
of but little value. This is because it so readih' de- 
teriorates in value and when used it has frequently 
lost much of its nitrogen by fermentation. When 
mixed with cow manure, both manures are improved, 
the rapid fermentation of the horse manure is checked, 
and at the same time the cow manure is improved in 
texture. It is estimated that horses void about three- 
fifths of their manure in the stable. A well-fed horse 
at ordinarily hard work will produce about 50 pounds 
of manure per day, of which about one-fourth is urine. 
A horse will produce about 6 tons of manure per year 
in the stable. If properly preserved and used it is a 
valuable, quick-acting manure, but if allowed to fer- 
ment and leach it will give poor results. 

183. Sheep Manure. — Sheep produce a small 
amount of concentrated manure, containing less water 
than that produced by any other domestic animal. It 
readily ferments and is a quick-acting fertilizer. 
When mixed with horse and cow manure the mixture 
ferments more evenly. Because of the small amount 
of water, sheep manure is very concentrated in composi- 
tion. It is valuable for general gardening purposes, or 
whenever a concentrated quick-acting manure is desired, 



154 SOII.S AND FERTILIZERS 

184. Hog Manure. — The composition of hog ma- 
nure is exceedingly variable on account of the varied 
character of the food consumed. The manure from 
fattening hogs which are well fed compares very fa- 
vorably in composition and value with the manure 
produced by other animals. It contains a high per 
cent, of water, and, like cow manure, may be slow 
in decomposing. From a given weight of grain, pigs 
produce less dry matter in the manure than sheep or 
cows. The liquid excrements of well-fed hogs 
are rich in nitrogen, containing, on an average, about 2 
per cent. On account of hog manure containing so 
much water, losses by leaching readily occur. The 
solid excrements when leached and deprived of the 
liquid excrements have but little value as a fertilizer. 

185. Hen Manure. — Like all other farm manures 
hen manure is variable in composition. The nitrogen 
is present mainly in the form of ammonium com- 
pounds. This makes it a quick-acting fertilizer. 
When fowds are well fed the manure contains about 
the same amount of nitrogen as sheep manure. Hen 
manure readily ferments, and if not properly cared 
for losses of nitrogen, as ammonia, occur. It is not 
advisable to mix hard wood ashes or ordinary lime 
with hen manure because the ammonia is so readily 
liberated by alkaline compounds. The value of hen 
manure is due to its being a quick-acting fertilizer 
rather than to its containing such a large amount of 



AGE AND KIND OF ANIMAL I55 

fertility. A hen produces about a bushel of manure 
per year. 55 

Composition of Hen Manure. 

Per cent. 

^^'^^^^ 57.50 

Nitrogen 127 

Phosphoric acid 0.82 

Potash 0.28 

186. Mixing of Solid and Liquid Excrements. — 

The solid and liquid excrements, when properly mixed, 
make a well-balanced manure. The urine alone is not 
a complete manure, as it is deficient in phosphoric acid 
and other mineral matter. The solid excrements and 
the urine, when mixed with soil, readily undergo nitri- 
fication. The nitrogen in the solid excrements is in 
the form of indigestible protein, and is rendered avail- 
able as plant food more slowly. I^and which has 
been heavily dressed with leached manure has re- 
ceived an unbalanced manure, and is deficient in 
nitrogen but fairly well supplied with mineral matter. 
Such a soil may fail to respond because of the unbal- 
anced character of the manure. 

187. Volatile Products from Manure. — The fer- 
mentation of manure in stables may cause the pro- 
duction of a large number of volatile compounds. The 
ammonia and nitrogen compounds are products w^hich 
cause losses of value to the manure. Urea, when it 
ferments, produces ammonia or ammonium carbonate. 
If ammonia is produced it combines with the carbon 



156 SOILS AND FERTILIZERS 

dioxide, which is always present in stables in liberal 
amounts as a product of respiration, and forms ammo- 
nium carbonate, a volatile compound. When the 
stable atmosphere becomes charged with ammonium 
carbonate, some of it is deposited on the walls of the 
stable, forming a white coating. The white coating 
found on harnesses and carriages stored in poorly ven- 
tilated stables, is ammonium carbonate. Accumula- 
tions of manure in the stable and poor ventilation are 
the conditions favorable to the production of this com- 
pound. 

188. Human Excrements. — The use of human ex- 
crements as manure is sometimes advised, and in some 
countries they are extensively used. When fresh, human 
excrements may contain a high per cent, of nitrogen 
and phosphoric acid ; when fermented, a loss of nitro- 
gen occurs. Heiden estimates that in a year 1,000 
pounds of excrements per person are made, which con- 
tain $2.25 worth of fertility. 5^ For sanitary reasons, 
human excrements should be used with great care. 
It is doubtful with the abundance and cheapness of 
plant food whether their extensive use as manure is 
advisable. About 1840, Liebig feared that the essen- 
tial elements of plant food would accumulate in the 
vicinity of large cities and be wasted, and that in time 
there would be a decline in fertility due to this cause.59 
Many political economists shared the same fear. 
Since that time the fixation of atmospheric nitrogen 



PRESERVATION OF MANURE I57 

through the agency of leguminous crops, the exten- 
sive beds of sodium nitrate, phosphate rock, and Stas- 
furt salts, have been discovered, and larger areas of 
more fertile soil have been brought under cultivation, 
so that it is not now considered so essential to devise 
means for utilizing human excrements as manure. 

THE PRESERVATION OF MANURE 

189. Leaching. — Leaching of manure is the great- 
est source of loss. Experiments by Roberts have 
shown that when horse manure is thrown in a loose 
pile and subjected to the joint action of leaching and 
weathering it may lose nearly 60 per cent, of its most 
valuable fertilizing constituents in six months. The 
tabular results are as follows :'5 

April 25. Sept. 28. Loss, 

^-bs. Lbs. Per cent. 

Gross weight 4,000 1,730 57 

Nitrogen 19.60 7.79 60 

Phosphoric acid . . 14.80 7 79 47 

Potash 36.0 8!65 76 

Value per ton ^2.80 |i.o6 

Cow manure, on account of its more compact nature, 
does not leach so readily as horse manure. A similar 
experiment with cow manure, conducted at the same 
time, showed the following losses : 

April 25. Sept. 28. Loss. 

Lbs. Lbs. Per cent. 

Gross weight 10,000 5,125 49 

Nitrogen 47 28 41 

Phosphoric acid • • 32 26 19 

Potash 48 44 8 

Value per ton I2.29 |i.6o 



158 SOILS AND FERTILIZERS 

When mixed cow and horse manure was compacted 
and "placed in a galvanized iron pan with a perfo- 
rated bottom" for six months, the losses were as fol- 
lows : 

March 29. Sept. 30. L,oss. 

Lbs. Lbs. Per cent. 

Gross weight 226 222 

Nitrogen 1.04 i.oi 3.2 

Phosphoric acid . . 0.61 0.58 4.7 

Potash 1.20 0.43 35.0 

Value per ton $2.38 12.16 

190. Losses by Fermentation. — When rapid fer- 
mentation takes place in manure, appreciable losses of 
nitrogen may occur. When the manure is well com- 
pacted and the pile is so constructed as to prevent the 
rapid circulation of air through the pile, the losses are 
reduced to the minimum. Experiments have shown 
that when leaching is prevented, the losses of nitrogen 
by the fermentation of mixed manure are very 
small. Under unfavorable conditions the losses 
by fermentation may exceed 15 per cent. Hen ma- 
nure, sheep manure, and horse manure suffer the 
greatest losses by rapid fermentation. When extreme 
conditions follow each other in succession, as exces- 
sive moisture, drought, and high temperature, then 
the greatest losses occur. 

191. Different Kinds of Fermentation. — The large 
number of organisms present in manure all belong to 
one of two classes : (i) aerobic, or (2) anaerobic. 
The aerobic ferments require an abundant supply of 



PRESERVATION OF MANURE 1 59 

air in order to carry on their work. When deprived 
of oxygen they become inactive. The anaerobic fer- 
ments require the opposite conditions. They become 
inactive in the presence of oxygen and can thrive only 
when air is excluded. In the center of a well-con- 
structed manure pile anaerobic fermentation takes 




Fig. 26. Fermentation of Manure. 

place while on the surface aerobic fermentation is act- 
ive. The anaerobic ferments prepare the way for the 
action of the aerobic bodies. When aerobic fermenta- 
tion is completed the organic matter is converted into 
water, carbon dioxide, ammonia, and allied gases. 
From what has been said regarding the action of these 
two classes of ferments it is evident that anaerobic 
fermentation is the most desirable. 

192. Water Necessary for Fermentation. — In order 
to produce the best results in fermenting manure 
water is necessary. If the manure becomes too dry 
abnormal fermentation takes place. Water is always 
beneficial on manure as long as leaching is prevented; 



l6o SOILS AND FERTILIZERS 

it encourages anaerobic fermentation by excluding the 
air. Excessive amounts of water, as that which falls 
on piles from the eaves of buildings, is more than is 
required for good fermentation. During a dry time it 
is beneficial, if conditions admit, to water the compost 
pile. 

193. Heat Produced during Fermentation. — Dur- 
ing the active fermentation of horse manure and sheep 
manure, a temperature of 175° F. may be reached by 
the fermenting mass. Ordinarily, however, the tem- 
perature of the manure pile ranges from 110° to 130° 
F. The highest temperature is reached near the sur- 
face where fermentation is most rapid. The tempera- 
ture of fermentation may be sufficiently high if the 
manure is mixed with the proper litter to cause spon- 
taneous combustion. 

194. Composting Manure May Improve Its Quality. 

— When manure is composted so that leaching and 
rapid fermentation do not take place the manure may 
be improved in quality by becoming more concentra- 
ted. Pound for pound, composted manure is more 
concentrated than fresh manure, because, if properly 
cared for, nearly all of the nitrogen, phosphoric acid, 
and potash of the original manure are obtained in a 
smaller bulk. A ton of composted manure is obtained 
from about 2,800 pounds of stable manure. 



PRESERVATION OF MANURE l6l 

Fresh Composted 

manure. manure. 

Per cent. Per cent. 

Nitrogen 0.50 0.60 

Phosphoric acid 0.28 0.39 

Potash 0.60 0.80 

In composting manure it should be the aim to in- 
duce anaerobic fermentation by excluding the air and 
retaining the water. This can be best accomplished 
by using mixed manure and making a compact pile, 
capable of shedding water. The compost pile should 
be shaded to secure better conditions for fermentation. 
If the pile becomes offensive a little earth on the sur- 
face will absorb the odors. 

195. Use of Preservatives. — The use of preserva- 
tives as gypsum and kainit have been recommended to 
prevent fermentation losses. Opinions differ as to 
their value. Moist gypsum, when it comes in contact 
with ammonium carbonate, produces ammonium sul- 
phate, a non-volatile compound, 

(NH ) CO 4- CaSO = (NH ) SO 4- CaCO . 

\ 4/2 3 • 4 V 4/2 4 ' 3 

Gypsum is used at the rate of about one-half pound 
per day for each animal. ^^ Experiments have shown 
that it may prevent a loss of 5 per cent, of the nitro- 
gen of horse manure. It may be safely sprinkled in 
the stalls as it has no action on the feet of animals. 
When gypsum is used as a fertilizer it is very desira- 
ble to use it in stables. It is not advisable to use 
lime in any other form than the sulphate. Unslaked 



l62 SOILS AND FERTILIZERS 

lime will decompose manure and liberate ammonia. 
Neither kainit nor gypsum should be used when ma- 
nure is exposed to the leaching action of rains. 
Preservatives cannot be made to take the place of 
want of care in handling manure ; they should be used 
only when the manure receives the best of care. 

196. Manure Produced in Covered Sheds and Box 
Stalls. — Manure produced under cover as in sheds 
and box stalls is of superior quality to that produced 
in any other way. Losses by leaching are avoided, 
the manure is compacted by the tramping of animals, 
and the solid and liquid excrements are more evenly 
mixed with the absorbents. By no other system is 
there such a large percentage of the fertility recovered. 
Manure from well-fed cattle, when collected and pre- 
pared in a covered shed, will have about the follow- 
ing composition : 

Per cent. 

Water 70.00 

Nitrogen 0.90 

Phosphoric acid 0.60 

Potash 0,70 

197. Value of Protected Manure. — Manure that 
is produced under cover has greater crop-produ- 
cing powers than manure that is cared for in any other 
way. Experiments by Kinnard show that such ma- 
nure produced 4 tons more potatoes per acre than pile 
manure, while 11 bushels more of wheat per acre 
were obtained from land which had the previous year 



THE USE OF MANURE 163 

received the covered manure than from land which 
received the uncovered manure.^' 

THE USE OF MANURE 

198. Direct Hauling to Fields. — It is always desir- 
able, whenever conditions allow, to draw the manure 
► directly to the field and spread it, rather than to allow 
it to accumulate about barns or in the barnyard. 
When taken directly to the field from the stable no 
losses by leaching occur, and the slight loss from 
fermentation and volatilization of the ammonia are 
more than compensated for by the benefits derived 
from the action of the fresh manure upon the soil. 
When manure undergoes fermentation in the soil, as 
previously stated it combines with the mineral matter 
of the soil and produces humates. The practice of 
hauling the manure directly to the field as soon as 
produced is the most economical way of caring for it. 
With scant rainfall, composting the manure before 
spreading is necessary, but with a liberal rainfall it is 
not essential. On a loam soil a direct application 
of stable manure is more advisable than on heavy clay 
or light sandy soils. On sandy soils there is frequently 
an insufficient supply of water to properly ferment the 
manure. Manure sometimes fails to show any benefi- 
cial effects the first year on heavy clay land, because 
of the slow rate of decomposition, but the second and 
third years the beneficial effects are noticeable. 



164 



SOILS AND FERTILIZERS 



199. Coarse Manure May Be Injurious. — The ap- 
plication of coarse leached manure may cause the soil 
to be so open and porous as to affect the water supply 
of the crop, by introducing, below the surface soil, a 
layer of straw, which breaks the capillary connection 
with the subsoil. Coarse manure and shallow spring 
plowing are frequently injurious, when fine or well- 
composted manure and fall plowing are beneficial. 
The injury resulting from the use of coarse manure is 
frequently due to its being allowed to leach before it is 
used, so that it does not properly ferment in the soil. 

200. Manuring Pasture Land. — In semiarid 
regions, where manure decomposes slowly, it is some- 
times advisable to spread it upon the pasture land as 




Fig. 27. Manured land. 

a top dressing. The manure encourages the growth 
of grass, which appropriates plant food otherwise lost, 
and it also acts as a mulch preventing excessive evapo- 
ration. Then when the pasture land is plowed and pre- 
pared for a grain crop it contains a better store of both 



THE USE OF MANURE 



l6^ 



water and available plant food. The manuring of 
pasture lands is one of the best ways of utilizing the 




Fig. 28. Unmanured land. 

manure when trouble arises from slow decomposition. 

201. Small Manure Piles Undesirable. — It is 

sometimes the custom to make a large number of 
small manure piles in fields. This is a poor practice, 
for it entails additional expense in spreading the ma- 
nure, and the small piles are usually so constructed 
that heavy losses occur, and the manure, when finally 
spread, is not uniform in composition. Oats grown on 
land manured in this way present an uneven appear- 
ance. There are small patches of thrifty, overfed 
oats, corresponding to the places occupied by the 
former manure piles, while large areas of half-starved 
oats may be observed. 

202. Rate of Application. — The amount of manure 
that should be applied depends upon the nature of the 
soil and the crop. On loam soils intended for general 
truck purposes heavier applications may be made than 
when grain is raised. For general farm purposes, 10 



l66 SOILS AND FERTILIZERS 

tons per acre are usually sufficient. It is better 
economy to make frequent light applications than 
heavier ones at long intervals. When manure is 
spread frequently the soil is kept in a more even state 
of fertility, and losses by percolation, denitrification, 
and ammonification are prevented. 

For growing garden crops 20 tons and more per acre 
are sometimes used. It is better, however, not to use 
stable manure too liberally for trucking, but to supple- 
ment it with special fertilizers as the crop may require. 
Soils which contain a large amount of calcium car- 
bonate admit of more frequent and heavier applications 
of manure than soils which are deficient in this com- 
pound. The lime aids fermentation and nitrification. 

203. Crops Most Suitable for Manuring. — Soils 
which contain a low stock of fertility will admit of 
manuring for the production of almost any crop. 
Soils well stocked with plant food, like some of the 
western prairie soils, which are in need of manure 
mainly for the physical action, will not admit of its 
direct use on all crops. On a prairie soil of average 
fertility an application of well-rotted manure will 
cause wheat to lodge. When it cannot be applied di- 
rectly to a crop, it may be used indirectly. It never 
injures corn by causing too rank a growth, and when 
wheat follows corn which has been manured there is 
but little danger of loss from lodging. 



THE USE OF MANURE 167 

On some soils stable manure cannot be used for 
growing sugar-beets ; on other soils it does not seem to 
exercise an injurious effect. Tobacco is injured as to 
quality by manure. Crops, as flax, tobacco, sugar- 
beets, and wheat, which do not admit of direct applica- 
tions of stable' manure all require the manuring of 
preceding crops. When in doubt as to what crop to 
apply the manure to, it is always safe to apply it to corn, 
and then to follow with the crop which would have 
been injured by its direct application. 

The fact that coarse, leached manure may cause 
trouble in a dry season, and that well-rotted manure 
may cause grain to lodge, are no substantial reasons 
why manure should be wasted as it frequently is in 
western farming by being burned, used for making 
roads, thrown away in streams, or used for filling up 
low places. 

204. Comparative Value of Manure and Crops.— 

The manure from a given amount of grain or fodder 
always gives better results than if the food itself were 
used directly as manure. The manure from a ton of 
bran will give better returns than if the bran itself 
were used. This is because so little of the fertilizing 
elements is extracted in the process of digestion and 
the action of the digestive fluids upon the food makes 
the manure more readily available as a fertilizer than 
the food which has not passed through any of the 
stages of fermentation. It is better economy to use 



l68 SOILS AND FERTILIZERS 

products as linseed meal and cottonseed meal for feed- 
ing stock, and take good care of the manure, than to 
use the materials directly. 

205. Lasting Effects of Manure. — No other ma- 
nures make themselves felt for so long a time as farm 
manures. In ordinary farm practice an application of 
stable manure will visibly affect the crops for a num- 
ber of years. At the Rothamsted Experiment Station, 
records have been kept for over fifty years as to the 
effects of manures upon soils. In one experiment 
manure was used for twenty years and then discon- 
tinued for the same period. It was observed that 
when its use was discontinued there was a gradual de- 
cline in crop-producing power, but not so rapid as on 
plots where no manure had been used. The manure 
which had been applied for the twenty-year period 
prior to its disuse made itself felt for an ensuing 
period of twenty years. 

206. Comparative Value of Manure Produced on 
Two Farms. — The fact that there is a great differ- 
ence in the composition and value of manures pro- 
duced on different farms may be observ^ed from the 
following examples : 

On. one farm 10 tons of timothy are fed. The 
liquid manure is not preserved and 25 per cent, of the 
remaining fertility is leached out of the solids, while 
5 per cent, of the nitrogen is lost by volatilization. 
It is estimated that half of the nitrogen and potash of 



THE USE OF MANURE 



169 



the food is voided in the urine. On account of the 
scant amount and poor quality of the food no milk or 
flesh is produced. 

On another farm 7.5 tons of clover hay and 2.5 tons 
of bran are fed. The liquid excrements are collected 





Fig. 29. Good manure. 



Fig. 30. Poor manure. 



and the manure is taken directly to the field and 
spread. It is estimated that 20 per cent, of the nitro- 
gen and 4 per cent, of the phosphoric acid and potash 
are utilized for the production of flesh or milk. 

The relative value of the manures from the two 
farms is as follows : 



Farm No. i. 



In 10 tons timothy. 
I.bs. 



Nitrogen 

Phosphoric acid . 
Potash 



250 

90 

400 



Loss in urine. 
250 -j- 2 = 125 lbs. nitrogen 
400 -j- 2 = 200 lbs. potash 



170 SOILS AND FERTILIZERS 

Loss by leaching. 
125 X 0.30 = 37.50 lbs. nitrogen 
90 X 0.25 ^ 22.50 lbs. phosphoric acid 
200 X 0.25 = 50 lbs. potash 

Total loss. 

Lbs. Per cent. 

Nitrogen 162.5 65 

Phosphoric acid 22.5 25 

Potash 250.0 62 

Present in final product, 
manure from i ton timothy. 

Lbs. 

Nitrogen 8.75 

Phosphoric acid 6.75 

Potash 15.00 

Relative money value |i.oo 

Farm No. 2. 

In 10 tons mixed feed. 
Lbs. 

Nitrogen 400 

Phosphoric acid 240 

Potash 300 

Loss, sold in milk and retained in body. 
Lbs. Per cent. 

Nitrogen, 400X0-20 80 20 

Phosphoric acid, estimated 10 4 

Potash 12 4 

Present in final product, 
manure from i ton feed. 

Lbs. 

Nitrogen 32.0 

Pho.sphoric acid 23.0 

Potash 26.0 

Relative money value fo-So 

207. Summary of Ways in which Stable Manure 
May Be Beneficial. — 

I. By adding new stores of plant food to the soil. 



THE USE OF MANURE 171 

2. By acting upon the soil, forming humates and 
rendering the inert plant food of the soil more availa- 
ble. 

3. By raising the temperature of the soil. 

4. By making the soil darker colored. 

5. By enabling soils to retain more water and to 
give it up gradually to growing crops. 

6. By improving the physical condition of sandy 
and clay soils. 

7. By preventing the denuding effects of heavy 
wind storms. 



CHAPTER VII 



PHOSPHATE FERTILIZERS 

208. Importance of Phosphorus as Plant Food. — 

Phosphorus in the form of phosphates is one of the 
essential elements of plant food. None of the higher 
orders of plants can complete their 
growth unless supplied with this 
element in some form. The illus- 
tration (Fig. 31) shows an oat plant 
which received no phosphates, but 
was supplied with all of the other 
elements of plant food. As soon as 
the phosphates stored up in the 
seed had been utilized, the plant 
ceased to grow, and after a few 
weeks died of phosphate starvation, 
having made the total growth 
shown in the illustration. All crops 
demand their phosphates at an early 
stage in their development. Wheat 
takes up eighty per cent, of its 
Oat planrgrown phosplioric acid in the first half of 
without phosphorus, ti^e growing period,36 while clover 

has assimilated all of its phosphoric acid by the 
time the plant reaches full bloom. ^^ Phosphates ac- 




Fig- 31- 



PHOSPHATE FERTILIZERS 1 73 

cumulate, to a great extent, in the seeds of all grains 
and are usually sold from the farm, especially when 
grain farming is extensively followed. All crops are 
very sensitive to the absence of phosphates; an imper- 
fect supply results in the production of light weight 
grains. The nitrogen and the phosphates are to a 
great extent stored up in the same parts of the plant, 
particularly in the seed, which is richer in both 
nitrogen and phosphorus than is any other part. 
Nitrogen is the chief element of protein, while phos- 
phorus is necessary to aid in transporting the pro- 
tein compounds through the cell walls of plants. 
In speaking of the phosphorus in plants and in fer- 
tilizers, as well as in soils, the term phosphoric acid 
or phosphoric anhydride is used. This is because 
phosphorus is an acid-forming element and, as already 
explained, the anhydride of the element is always con- 
sidered instead of the element itself. 

209. Amount of Phosphoric Acid Removed in 
Crops. — The amount of phosphoric acid removed 
in an acre of different farm crops ranges from 18 to 30 
pounds : 

Phosphoric acid 
per acre. 

Lbs. 

Wheat, 20 bu 12.5 

Straw, 2,000 lbs 7.5 

Total 20.0 



174 SOILS AND FERTILIZERS 

Phosphoric acid 
per acre. 

Lbs. 

Barley, 40 bu .... 15 

Straw, 3,000 lbs 5 

Total 20 

Oats, 50 bu 12 

Straw, 3,000 lbs 6 

Total 18 

Corn, 65 bu 18 

Stalks, 4,000 lbs 4 

Total 22 

Peas, 3,500 lbs 25 

Red clover, 4,000 lbs < 28 

Potatoes, 150 bu 20 

Flax, 15 bu 15 

Straw, 1,800 lbs 3 

Total...' 18 

210. Amount of Phosphoric Acid in Soils. — To 

meet the demand of growing crops (for 25 ponnds of 
phosphoric acid per acre), there is present in soils from 
1,000, and less, to 8,000 pounds of phosphoric acid per 
acre, of which, however, only a fraction is available as 
plant food at any one time. The availability of phos- 
phoric acid is a factor which has a great deal to do in 
determining crop-producing power. Many soils contain 
a large amount of total phosphoric acid, which has be- 
come unavailable because of poor cultivation and the 



PHOSPHATE FERTILIZERS 1 75 

absence of stable manure and lime to combine with 
the phosphates and render them available. 

211. Source of Phosphoric Acid in Soils.— The 
phosphates found in soils are derived mainly from the 
disintegration of phosphate rock, and from the remains 
of animal life. The phosphate deposits found in various 
localities are supposed to have been derived either 
from the remains of marine animals or from sea-water 
highly charged with soluble phosphates. These de- 
posits have been subjected to various geological and 
climatic changes which have resulted in the formation 
of soft phosphate, pebble phosphate, and rock phos- 
phate.^^ 

212. Commercial Forms of Phosphoric Acid.— The 

commercial sources of phosphate fertilizers are (i) 
phosphate rock, (2) bones and bone preparations, (3) 
phosphate slag, and (4) guano. With the exception 
of phosphate slag and guano, the prevailing form of 
the phosphorus is tricalcium phosphate. Before be- 
ing used for commercial purposes, the tricalcium 
phosphate, which is insoluble and unavailable, is 
treated with sulphuric acid which produces monocal- 
cium phosphate, a soluble and available form of plant 
food. 

Ca3(P0J, + 2H SO, + 5HP = CaH (PO,), + HO + 

2CaS0.2HO. 

4 2 

In making phosphate fertilizers from bones or phos- 



176 SOILS AND FERTILIZERS 

phate rock an excess of the rock is used so that there 
will be no free acid to be injurious to vegetation. 

213. Different Forms of Calcium Phosphate. — 
The usual form in which calcium phosphate is found 
in nature is tricalcium phosphate, Ca (PO )^. Unless 
associated with organic matter or salts which render 
it soluble it is of but little value as plant food. When 
tricalcium phosphate is treated with sulphuric acid, 
monocalcium phosphate, CaH (PO )^, is formed. This 
compound is soluble in water and directly available as 
plant food. When tricalcium and monocalcium phos- 
phate are brought together in a moist condition, di- 
calcium phosphate is produced. 

Ca/PO,), + CaH/PO^)^ = 2Ca H,(PO;,. 

Another form of phosphate of lime, met with in basic 
phosphate slag, is tetracalcium phosphate, (CaO) P^O . 

214. Reverted Phosphoric Acid. — When mono- 
and tricalcium phosphate react, the product is known 
as reverted phosphoric acid, which is insoluble in 
water, but is not in such form as to be unavailable as 
plant food. It is generally considered that the re- 
verted phosphoric acid is available as plant food : it is 
soluble in a dilute solution of ammonium citrate, and 
is sometimes spoken of as citrate-soluble phosphoric 
acid. Citrate-soluble phosphoric acid may also be 
formed by the action upon the monocalcium phos- 
phate of iron and aluminum compounds present as 



PHOSPHATE FERTILIZERS 1 77 

impurities in the phosphate rock. This process is a 
fixation change, as described in Chapter V. In an old 
fertilizer there may be present citrate-soluble phos- 
phoric acid in two forms, as dicalcium phosphate and 
as hydrated phosphates of iron and aluminum. The 
citrate-soluble phosphoric acid in fertilizers is not all 
equally valuable as plant food because of the different 
phosphate compounds that may be dissolved. 

215. Available Phosphoric Acid. — As applied to 
fertilizers, the term available phosphoric acid includes 
the water-soluble and citrate-soluble phosphoric acid. 
These solvents do not, under all conditions, make a 
sharp distinction as to the available and unavailable 
phosphoric acid when it comes to plant growth. Some 
forms of bones, which are insoluble in an ammonium 
citrate solution are available as plant food, and then 
again some forms of aluminum phosphate which are 
soluble are of but little value as plant food. The 
terms available and unavailable phosphoric acid, as 
applied to commercial fertilizers, refer to the solubility 
of the phosphates, and as a general rule their value as 
plant food is in accord with their solubilities. The 
more insoluble the less valuable the material. 

216. Phosphate Rock. — Phosphate rock is found 
in many parts of the United States, particularly in 
South Carolina, North Carolina, Florida, Virginia, 
and Tennessee. The deposits occur in stratified 
veins, as well as in beds and pockets. There are dif- 



lyS SOILS AND FERTILIZERS 

ferent types of phosphates as hard rock, soft rock, land 
pebble, and river pebble. The pebble phosphates are 
found either on land or collected in cavities in the 
water courses, and are generally spherical masses of 
variable size. The soft rock phosphate is easily 
crushed, while the hard rock requires pulverizing with 
rock crushers. Phosphate rock usually contains from 
40 to 70 per cent, of calcium phosphate, the equiva- 
lent of from 17 to 30 per cent, phosphoric acid. The 
remaining 30 to 60 per cent, is composed of fine sand, 
limestone, alumina and iron compounds, with other 
impurities, which often render a phosphate unsuitable 
for manufacturing high-grade fertilizer. Raw phos- 
phate rock is usually sold at the mines for $1.75 to 
$4.50 per ton. 

217. Superphosphate. — Pulverized rock phosphate 
known as phosphate flour, is treated with commercial 
sulphuric acid and soluble monocalcium phosphate 
obtained. The amount of sulphuric acid used is de- 
termined from the composition of the rock. Impuri- 
ties as calcium carbonate and calcium fluoride react 
with sulphuric acid and cause a loss of acid. Ordi- 
narily, a ton of high-grade phosphate rock requires a 
ton of sulphuric acid. The mixing is usually done in 
lead-lined tanks. A weighed amount of phosphate 
flour is placed in the tank, and the sulphuric acid 
added, through lead pipes, from the acid tower. The 
mixing of the acid and phosphate is done with a me- 



PHOSPHATE FERTILIZERS 179 

chanical mixer, driven by machinery. From the 
mixer the material is passed into large tanks, where 
two or three days are allowed for the completion of 
the reaction. When the mass solidifies, it is ground 
and sold as superphosphate. In the manufacture of 
superphosphate, gypsum (CaSO .2H^0) is always pro- 
duced. A ton of superphosphate prepared from high- 
grade rock in the way outlined will contain about 40 
per cent, of lime phosphates, equivalent to 18 per cent, 
phosphoric acid. If a poorer quality of rock is used a 
proportionally smaller amount of phosphoric acid is 
obtained. A more concentrated superphosphate is ob- 
tained by producing -phosphoric acid from the phos- 
phate rock, and then allowing the phosphoric acid to 
act upon fresh portions of the rock, the reactions be- 
ing as follows :^3 

Ca3(P0,X + SH.SO^ = 3CaS0^ + aH^CPO^), 
Ca/POJ, + 4H3PO^ + 3H O = 3[CaH/P0J,.H O]. 
Ca3(PO;, + 2H P0^+i2H O = 3[Ca H^(P0^X.4H O]. 

The phosphoric acid is separated from the gypsum be- 
fore acting upon the phosphate flour. In this way, 
superphosphate containing from 35 to 45 per cent. 
of phosphoric acid is produced. When fertilizers are 
to be transported long distances this concentrated prod- 
uct is preferable. The terms 'acid' and 'superphosphate' 
are generally used to designate both the first product 
formed by the action of sulphuric acid and that pro- 



l8o SOILS AND FERTILIZERS 

duced by the phosphoric acid but of late there is a ten- 
dency to restrict the term 'acid phosphate' to the 
product formed by the action of sulphuric acid, and 
the term 'super-phosphate' to the concentrated product 
formed by the action of phosphoric acid. 

2i8. Commercial Value of Phosphoric Acid. — The 

commercial value of phosphoric acid in fertilizers is 
determined by the value of the crude phosphate rock, 
cost of grinding and treating with sulphuric acid, and 
cost of transportation. The price of phosphoric acid 
in superphosphates usually ranges from 5 to 6 cents 
per pound. The field value, that is the increased 
yields obtained from the use of superphosphates, may 
not be in accord with the commercial value because so 
many conditions govern its use. The phosphoric acid 
obtained from feed-stuffs is usually considered worth 
about a cent a pound less than that from superphos- 
phates. Water-soluble phosphoric acid is generally 
rated a half cent per pound higher than citrate-soluble 
phosphoric acid. 

219. Phosphate Slag. — In the refining of iron ores 
by the Bessemer process, the phosphorus in the iron is 
removed as a basic slag. The lime, which is used as a 
flux, melts and combines with the phosphorus of the 
ore, forming phosphate of lime. The slag has a varia- 
ble composition. The process by which the phos- 
phorus of pig iron is removed and converted into basic 
phosphate slag is known as the Thomas process, and 



PHOSPHATE FERTILIZERS l8l 

the product is sometimes called Thomas' slag. At the 
present time but little basic slag is produced for fer- 
tilizer purposes in this country. In Germany and 
some other European countries the amount used is 
nearly equal to the amount of superphosphate. Phos- 
phate slag is ground to a fine powder and is applied 
directly to the land, without undergoing the sulphuric 
acid treatment. Phosphoric acid is present mainly in 
the form of tetracalcium phosphate, (CaO) P^O . 

220. Guano is the Spanish for dung, and is a concen- 
trated form of nitrogenous and phosphate manure of 
interest mainly on account of its historic significance. 
It is a mixture of sea-fowl droppings which have ac- 
cumulated along the seacoast in sheltered regions. 
The mixture of dung, dead animals, and debris, has 
undergone fermentation, and is concentrated in both 
nitrogen and phosphoric acid. The introduction of 
guano into Europe marked an important period in agri- 
culture, inasmuch as its use demonstrated the action 
and importance of concentrated fertilizers. All of the 
best beds of guano have been exhausted and only a 
little of the poorer grades are now found on the mar- 
ket. The best qualities of guano contained from 12 
to 15 per cent, of phosphoric acid, 10 to 12 per cent, 
of nitrogen, and from 5 to 7 per cent, of alkaline salts. 

BONE FERTILIZERS 

221. Raw Bones contain, in addition to phosphate 
of lime, Ca^(POJ^, organic matter which makes them 



l82 SOILS AND FERTILIZERS 

slow in decomposing and slow in their action as a fer- 
tilizer. Before being nsed as fertilizer they shonld be fer- 
mented in a compost heap with wood ashes in the fol- 
lowing way : A protected place is selected so that no 
losses from drainage will occur. A layer of well-com- 
pacted manure is covered with wood ashes, the bones 
are then added and well covered with manure and 
wood ashes. From three to six months should be al- 
lowed for the bones to ferment. The large, coarse 
pieces may then be crushed and are ready for use. 
^he presence of fatty material in a fertilizer retards its 
action because fat is so slow in decomposing. Bones 
from which the organic matter has been removed are 
more active as a fertilizer than raw bones. Bones 
contain from i8 to 25 per cent, of phosphoric acid and 
from 2 to 4 per cent, of nitrogen. The amount and 
value of the citrate-soluble phosphoric acid in bones 
are extremely variable. 

222. Bone Ash is the product obtained when bones 
are burned. It is not extensively used as a fertilizer 
because of the greater commercial value of bone-black. 
It contains about 36 per cent, of phosphoric acid, and 
is more concentrated than raw bones. 

223. Steamed Bones. — Raw bones are subjected to 
superheated steam to remove the fat and ossean which 
are used for making soap and glue; they are then pul- 
verized and sold as fertilizer under the name of bone 
meal, which contains from 1.5 to 2.5 per cent, of nitro- 



BONE FERTII.IZERS 1 83 

gen and from 22 to 29 per cent, of phosphoric acid. 
Steamed bones make a more active fertilizer than raw 
bones. Occasionally, well-prepared bone meal is used 
for feeding pigs and fattening stock in the same way 
that flesh meal is used. 

224. Dissolved Bone. — When bones are treated 
with sulphuric acid as in the manufacture of super- 
phosphates the product is called dissolved bone. The 
tricalcium phosphate undergoes a change to more 
available forms, as described, and the nitrogen is ren- 
dered more available. Dissolved bone contains from 
2 to 3 per cent, of nitrogen and from 15 to 17 per 
cent, of phosphoric acid. 

225. Bone-black. — When bones are distilled bone- 
black is obtained. It is extensively employed for re- 
fining sugar, and after it has been used and lost its 
power of decolorizing solutions, it is sold as fertilizer. 
It contains about 30 per cent, phosphoric acid and is a 
concentrated phosphate fertilizer. 

226. Use of Phosphate Fertilizers. — The amount 
of phosphoric acid advisable to apply to crops, varies 
with the nature of the soil and the kind of crop to be pro- 
duced. On a poor soil 400 pounds of superphosphate 
per acre is an average application. It is usually ap- 
plied as a top dressing just before seeding, and maybe 
placed near the hills of corn or potatoes, but not in 
contact with the seed. It is not advisable to make 
heavy applications of superphosphates at long inter- 



l84 SOILS AND FERTILIZERS 

vals, because the process of fixation may take place to 
such an extent that crops are unable to utilize the fer- 
tilizer. Lighter and more frequent applications are 
preferable. Phosphates should not be mixed with 
lime carbonate or with loam before spreading.^' It is 
best to apply the fertilizer directly to the land. Phos- 
phates may be used in connection with farm manures. 
Many soils which contain liberal amounts of total 
phosphoric acid are improved with a light dressing of 
superphosphates. Such soils, however, should be more 
thoroughly cultivated, and manured with farm ma- 
nures, to make the phosphates available. There is 
frequently an apparent lack of phosphoric acid in the 
soil when in reality the trouble is due to other causes, 
as lack of organic matter to combine with the phos- 
phates or to a deficiency of lime. Before using phos- 
phate fertilizers, careful field tests should be made to 
determine if the soil is in actual need of available 
phosphoric acid. Directions for making these tests 
are given in Chapter X. 

227. How to Keep the Phosphoric Acid Available. 

— Phosphoric acid associated with organic matter in 
a moderately alkaline soil, is more available than that 
in acid soils. Soft phosphate rock may be mixed with 
manure or materials like cottonseed meal and made 
slowly available for crops. Soils which have a good 
stock of phosphoric acid, when kept well manured, 
and occasionally limed if necessary, contain a lib- 



BONE FERTILIZERS 185 

eral supply of available phosphoric acid. As an illus- 
tration, the following example of two soils from ad- 
joining farms, which have been cropped and manured 
differently, may be cited :^° 

Soil well manured No manure and 

and crops continuous wheat 

rotated. raising. 

Per cent. Per cent. 
Total phosphoric acid ... . 0.20 0.20 

Humus 4.25 1.62 

Humic phosphoric acid .. 0.06 0.02 

- It is more economical to keep the insoluble phos- 
phoric acid of the soil in available forms by the use of 
farm manures than it is to purchase superphosphates. 



CHAPTER VIII 



POTASH FERTILIZERS 

228. Potassium an Essential Element of Plant 
Food. — Potassium is oue of the three elements most 

essential as plant food. When it is 
removed from a soil plants are un- 
able to develop. Oats seeded in a 
soil from which the potash only 
had been extracted made the total 
growth shown in the illustration 
(Fig. 32). When potash is present 
in the soil in liberal amounts vig- 
orous plants are produced. Potash, 
like phosphoric acid and nitrogen, 
is utilized by crops in the early 
stages of growth. Potassium does 
not accumulate in seeds to the same 
extent as phosphoric acid and nitro- 
gen, but is present mainly in stems 
and leaves, consequently when 

Fio-. 32. Oat plant straw CrOpS are utilized in pro- 
grown without potash, ducing manure the potash is not 
lost or sold from the farm. But with ordinary grain 
farming excessive losses of potash do occur, particu- 
larly when the straw is burned and the ashes are wasted. 




POTASH FKRTII.IZERS 1 87 

229. Amount of Potash Removed in Crops. — In 

grain crops from 35 to 60 pounds of potash per acre 
are removed from the soil. For grass crops more pot- 
ash is required than for grains, while roots and tubers 
require more than grass. The approximate amount of 
potash removed in various crops is given in the fol- 
lowing table :37 

Potash per acre. 
Lbs. 

Wheat, 20 bu 7 

Straw, 2,000 lbs 28 

Total 35 

Barley, 40 bu 8 

Straw, 3,000 lbs 30 

Total 38 

Oats, 50 bu 10 

Straw, 3,000 lbs 35 

Total 45 

Corn, 65 bu 15 

Stalks, 3.000 lbs 45 

Total 60 

Peas, 30 bu 22 

Straw, 3,500 lbs 38 

Total 60 

Flax, 15 bu 19 

Straw, 1,800 lbs 8 

Total 27 



l88 SOILS AND FERTILIZERS 

Mangels, lo tons 150 

Meadow hay, i ton 45 

Clover hay, 2 tons . 66 

Potatoes, 150 bushels 75 

230. Amount of Potash in Soils. — In ordinary 
soils there are from 3,500 to 12,000 pounds of potash 
per acre to the depth of one foot. Many soils with 
apparently a good stock of total potash give excellent 
results when a light dressing of potash salts is applied. 
The amount of available potash in the soil is more 
difficult to estimate than the available phosphoric 
acid. There is also a great difference in crops as to 
their power of obtaining potash. Some require 
greater help in procuring this element than others. A 
lack of available potash is sometimes indirectly due to 
a deficiency of other alkaline matter in the soil, which 
prevents the necessary changes taking place in order 
that the potash may be liberated as plant food. 

231. Sources of Potash in Soils. — The main 
source of the soil potash is feldspar, which, after dis- 
integration, is broken up into kaolin and potash com- 
pounds. Mica and granite also, in some localities, 
contribute liberal amounts. The most valuable forms 
of potash are the zeolitic silicates. The amount of 
water-soluble potash, except in alkaline soils, is ex- 
tremely small. By the action of many fertilizers the 
potash compounds undergo changes in composition. 
For example, the gypsum which is always present in 



STASSFURT SALTS 1 89 

acid phosphates, liberates some potash. The potash 
compounds of the soil are in various degrees of com- 
plexity from forms soluble in dilute acids to insoluble 
minerals as feldspar. 

232. Commercial Forms of Potash. — Prior to the 
introduction of the Stassfurt salts, wood ashes were 
the main source of potash. Since the discovery and 
development of the Stassfurt mines, the natural prod- 
ucts as kainit, and muriate and sulphate of potash have 
been extensively used for fertilizing purposes. A 
small amount of potash is also obtained from waste 
products as tobacco stems, cottonseed hulls, and the 
refuse from beet-sugar factories. 

STASSFURT SALTS 

233. Occurrence.^3 — i^he Stassfurt mines were first 
worked with the view of procuring rock salt. The 
presence of the various compounds of potash, soda, and 
magnesia, associated with the layers of rock salt, were 
regarded as troublesome impurities, and attempts were 
made by sinking new shafts to avoid them, but with 
the result of finding them in greater abundance. 
About 1864 their value as potash fertilizers was es- 
tablished. The mines are now owned and worked by 
a syndicate. It is supposed that at one time the 
region about the mines was submerged and filled with 
sea-water. The tropical climate of that geological period 
caused rapid evaporation, which resulted in forming 
mineral deposits, the less soluble material as lime sul- 



I go SOILS AND FERTILIZERS 

phate being first deposited, then a layer of rock salt, 
and finally layers of potash and magnesium salts in 
the order of their solubility. 

234. Kainit is a mineral composed of potassium 
sulphate, magnesium sulphate, magnesium chloride, 
and water of cr}'Stallization. As it comes from the 
mine it is mixed with gypsum, salt, potassium chlo- 
ride, and other bodies. Kainit contains from 1 2 to 1 2. 50 
per cent, of potash, and is one of the most important 
of the Stassfurt salts. It is extensively used as a pot- 
ash fertilizer, and is also mixed with other materials 
and sold as a commercial fertilizer. The magnesium 
chloride causes it to absorb water, and the presence of 
other compounds results in the formation of hard 
lumps, whenever kainit is kept for a long time. 
Kainit is soluble in water, and can be used as a top 
dressing at the rate of 75 to 200 pounds or more per acre. 

235. Sulphate of Potash. — High-grade sulphate 
of potash is prepared from some of the crude Stassfurt 
salts, and may contain as high as 97 per cent. K^SO . 
Low-grade sulphate of potash is about 90 per cent, 
pure. High-grade sulphate of potash contains about 
50 per cent, of potassium oxide (K^O), and is one of 
the most concentrated forms of potash fertilizer. It 
is particularly valuable because it can be safely used on 
crops as tobacco and potatoes which would be injured 
in quality if muriate of potash were applied, or if 
much chlorine were present. 



STASSFURT SALTS 191 

236. Miscellaneous Potash Salts. — Carnallit, 9 
per cent. K^, — composed of KCl.MgC1^.6Hp. 
Polyhalit, 15 per cent. K^O, — composed of K^SO .Mg 
SO .(CaSO )^.H^0. Krugit, 10 per cent. K^O, — com- 
posed of K's6^.MgS0^.(CaS0j^.Hp. Sylvinit, 16 
to 20 per cent. K^O, — composed of KCl.NaCl and 
impurities. Kieserit, 7 per cent. K^O, — composed of 
MgSO and carnallit. 

237. Wood Ashes. — For ordinary' agricultural pur- 
poses, wood ashes are the most important source of 
potash. Ashes are exceedingly variable in composi- 
tion. When leached the soluble salts are extracted 
and there is left only about i per cent, of potash. In 
unleached ashes the amount of potash ranges from 2 
to 10 per cent. Soft wood ashes contain much less 
potash than hard wood ashes. Goessmann gives the 
following as the average of 97 samples of ashes :^^ 

Average conipositiou. Range. 

Per cent. Per cent. 

Potash 5.5 2.5 to 10.2 

Pho.sphoric acid 1.9 0.3 to 4.0 

Lime 34.3 18.0 to 50.9 

In 10,000 pounds of wood. Potash. Phosphoric acid. 

Lbs. Lbs. 

White oak 10.6 2.5 

Red oak 14.0 6.0 

Ash 15.0 I.I 

Pine 0.8 0.7 

Georgia pine 5.0 1.2 

Dogwood 9.0 5.7 



192 SOILS AND FERTILIZERS 

238. Action of Ashes on Soils. — In ashes, the pot- 
ash is present mainly as potassium carbonate. Ashes 
are usually regarded as a potash fertilizer only, but 
they also contain lime and phosphoric acid, and may 
be very beneficial in supplying these elements. They 
are valuable too because they add alkaline matter to 
the soil, which corrects acidity and aids nitrification. 
A dressing of ashes improves the mechanical condi- 
tion of many soils by binding together the soil parti- 
cles. This property is well illustrated in the so-called 
"Gumbo" soils, which contain so much alkaline mat- 
ter that the soil has a soapy taste and feel, and when 
plowed the particles fail to separate. 

239. Leached Ashes. — When ashes are leached the 
soluble salts are extracted, and the insoluble matter 
which is left is composed mainly of calcium carbonate 
and silica. ^5 

Unleached ashes. Leached ashes. 

Per cent. Per cent. 

Water 12.0 30.0 

Silica, etc 13.0 13.0 

Potassium carbonate 5.5 i.i 

Calcium " 61.0 51.0 

Phosphoric acid 1.9 1.4 

240. Alkalinity of Leached and Unleached Ashes. 

— A good way to detect leached ashes is to deter- 
mine the alkalinity in the following way : Weigh 
out 2 grams of ashes into a beaker, add 100 cc. dis- 
tilled water, and heat on a sand-bath nearly to boiling, 



STASSFURT SALTS 193 

cool, and filter. To 50 cc. of the filtrate add about 3 
drops of cochineal indicator, and then a standard solu- 
tion of hydrochloric acid from a burette until the solu- 
tion is neutral. If a standard solution of acid cannot 
be procured, one containing 15 cc. concentrated hydro- 
-chloric acid per liter of distilled water may be used for 
comparative purposes. Leached ashes require less than 
2 cc. of acid to neutralize the alkaline matter in i gram 
while unleached ashes require from 10 to 18 cc. In pur- 
chasing wood ashes, if a chemical analysis cannot be 
secured, the alkalinity of the ash should be determined. 
241. Coal and Other Ashes. —Since the amount of 
phosphoric acid and potash in coal ashes is very small, 
they have but little fertilizer value. Soft-coal ashes con- 
tain more potash than those from hard coal, but it is held 
in such forms of combination as to be of but little value. 
The ashes from sawmills where soft wood is burned 
and the ashes are unprotected, are nearly worthless. 
When peat-bogs are burned over, large amounts of ashes 
are produced. If the bogs are covered with timber, 
the ashes are sometimes of sufficient value to warrant 
their transportation and use. 

Phosphoric 
Potash. acid. 

Perceut. Percent. 

Hard coal o.io 010 

Soft coal 0.40 0.40 

Sawmill ashes'^ 1,20 i cxd 

Peat-bog ashes'^ 1.15 054 

Peat-bogashes (timbered)'^ 3.68 2.56 

Tobacco stems 4.00 7^00 

Cottonseed hulls 20.00 7.00 



194 SOILS AND FERTILIZERS 

242. Commercial Value of Potash. — The market 
value of potash is determined from the selling price of 
high-grade sulphate of potash and kainit. Ordinarily, 
the price per pound of potash varies from 4 to 5 cents. 
As in the case of both nitrogen and phosphoric acid, 
the market and the field values may be entirely at 
variance. Before potash salts are used, careful field 
tests should be made to determine the actual condi- 
tion of the soil as to its needs in potash. 

243. Use of Potash Fertilizers. — Wood ashes, or 
Stassfurt salts, should not be used in excessive 
amounts. Not more than 300 pounds per acre should 
be applied unless the soil is known to be markedly de- 
ficient, and previous tests indicate that larger amounts 
are safe and advisable. Potash fertilizers should be 
evenly spread and not allowed to come in contact with 
plant tissue. They should be used early in the spring 
before seeding or before the crop has made much 
growth. Wood ashes make an excellent top dressing 
for grass lands, particularly where it is desired to en- 
courage the growth of clover. There are but few 
crops or soils that are not greatly benefited by a light 
application of wood ashes, and none should ever be 
allowed to leach or waste about a farm. 

When a potash fertilizer is used, a dressing of lime 
will frequently be beneficial. The potash undergoes 
fixation, and when it is liberated there should be some 
basic material as lime to take its place. Goessmann 



STASSFURT SALTS I95 

observed that land manured for several years with 
potassium chloride finally produced sickly crops, but 
that an application of slaked lime restored a healthy 
appearance to succeeding crops.^^ If the soil is well 
stocked with lime its joint use with potash fertilizers 
is not necessary. 



CHAPTER IX 



LIME AND MISCELLANEOUS FERTILIZERS 

244. Calcium an Essential Element of Plant Food. 

— Calcium is present in the ash of all plants, and is 
nsnally more abundant in soils than phosphorus or 

potassium. It takes an essential 
part in plant growth, and when- 
ever withheld growth is checked. 
The effect of removing calcium 
from the soil is shown in the illus- 
tration (Fig. ^1,)^ which gives the 
total growth made by an oat plant 
under such a condition. 

Plants grown on soils deficient 
in calcium compounds, lack hard- 
iness. They are not so able to 
withstand drought, or climatic 
changes, as plants grown on soils 
well supplied with this element. 
Calcium does not accumulate 
in the seeds of plants, but is pres- 
ent mainly in the leaves and 
stems where it takes an impor- 
tant part in the production of new 
tissue. The term lime is used in 
speaking of the calcium oxide content of soils and crops. 




i^'ig- 33- 

Oat plant grown with- 
out lime. 



LIME AND MIvSCELLANEOUS FERTILIZERS 197 

245. Amount of Lime Removed in Crops. 37 — 

Pounds per acre. 

Wheat, 20 bushels i 

Straw, 2000 pounds 7 

Total 8 

Corn, 65 bushels i 

Stalks, 3000 pounds 11 

Total 12 

Peas, 30 bushels 4 

Straw, 3500 pounds 71 

Total 75 

Flax, 15 bushels 3 

Straw, 1800 pounds 13 

Total 16 

Clover, 4000 pounds 75 

Clover and peas remove so much lime from the soil 
that they are often called lime plants. The amount 
required by grain and hay is small compared with that 
required for a clover or pea crop. 

246. Amount of Lime in Soils. — There is no ele- 
ment in the soil in such variable amounts as calcium. 
It may be present from a few hundredths of a per cent, 
to twenty per cent.; soils which contain from 0.4 to 
0.5 per cent, are usually well supplied. The lime in 
a soil takes an important part in soil fertility ; when 
deficient, humic acid may be formed, nitrification 
checked,and the soil particles will lack binding material. 



198 SOILS AND FERTILIZERS 

247. Different Kinds of Lime Fertilizers. — By the 

term 'lime fertilizer' is usually meant land plaster 
(CaSO .2H^0). Occasionally quicklime (CaO) and 
slaked lime (Ca(OH)^) are used on exceedingly sour 
land. In general a lime fertilizer is one which sup- 
plies the element calcium ; common usage, however, 
has restricted the term to sulphate of lime. 

248. Action of Lime Fertilizers upon Soils. — Lime 
fertilizers act both chemically and physically. Chem- 
ically, lime unites with the organic matter to form 
humate of lime and prevent the formation of humic 
acid. It aids in nitrification and acts upon the soil, 
liberating potassium and other elements of plant food. 
Physically, lime improves capillarity, precipitates clay 
when suspended in water, and prevents losses, as the 
washing away of fine earth. 

249. Action of Lime upon Organic Matter. — When 
soils are deficient in lime, an acid condition may de- 
velop to such an extent as to be injurious to vegeta- 
tion. In fact nitrogen, phosphoric acid, and potash 
may all be present in liberal amounts, but in the 
absence of lime poor results will be obtained. Ex- 
periments at the Rhode Island Experiment Station 
indicate that there are large areas of acid soils in the 
Eastern States which are much improved when treated 
with air-slaked lime.^^ There is a great difference in 
the power of plants to live in acid soils. Agricultural 
plants are particularly sensitive, while many weeds 



LIME AND MISCELLANEOUS FERTILIZERS 199 

have such strong power of endurance that they are 
able to thrive in the presence of acids. The charac- 
ter of the weeds frequently reflects the character of the 
soil as to acidity, in the same way that an "alkali" 
soil is indicated by the plants produced. 

250. Lime Liberates Potash. — The action of lime 
upon soils well stocked with potash results in the fixa- 
tion of the lime and the liberation of the potash ; the 
reaction takes place in accord with the well-known 
exchange of bases. The extent to which potash may 
be liberated by lime depends upon the firmness with 
which the potash is held in the soil. Boussingault 
found that when clover was limed there was present 
in the crop three times as much potash as in a similar 
crop not limed. His results are as follows : ^^ 

Kilos per hectare. 
In crop not limed. In limed crop. 

First Second First Second 

year. year. year. year. 

Lime' 32.2 32.2 79.4 102.8 

Potash 26.7 28.6 95.6 97.2 

Phosphoric acid, ii.o 7.0 24.2 22.9 

The indirect action of land plaster upon Western 
prairie soils in liberating plant food, particularly 
potash and phosphoric acid, is unusually marked. 
Laboratory experiments show that small amounts of 
gypsum are quite active in rendering potash, phos- 
phoric acid, and even nitrogen soluble in the soil 
water. 5 



200 SOILS AND FERTILIZERS 

251. Quicklime and Slaked Lime. — When it is de- 
sired to correct acidity slaked lime is used. Air- 
slaked lime is not as valuable as water-slaked lime. 
Quicklime cannot be used on land after a crop has 
been seeded. Both slaked lime and quicklime 
should be applied some little time before seed- 
ing and not to the crops. The action of quicklime 
upon organic matter is so rapid that it destroys vege- 
tation. Slaked lime is less injurious to vegetation. 

252. Pulverized Lime Rock. — In some localities 
pulverized lime rock is used. It may be applied as a 
top-dressing in almost unlimited amounts. It is most 
beneficial on light, sandy soils, where it performs the 
function of fine clay as well as being beneficial in its 
chemical action. Not all soils are alike responsive to 
applications of limestone, and before using, it is best 
to determine to what extent it will be beneficial. 
There are no conditions where limestone is injurious 
to soil or crop. 

253. Marl. — Underlying beds of peat, deposits of 
marl are occasionally found. Marl is a mixture of 
disintegrated limestone and clay, and contains varia- 
ble amounts of calcium carbonate, phosphoric acid, 
and potash. When peat and marl are found together 
they may be used jointly with manure as described in 
Section 175. Many sandy lands in the vicinity of peat 
and marl deposits would be greatly improved, both 
physically and chemically, by the use of these materials. 



LIME AND MISCELLANEOUS FERTILIZERS 20I 

254. Physical Action of Lime. — The addition of 
lime fertilizers to sandy soils improves their general 
physical condition. Heavy clays lose their plasticity 
when limed ; the fine clay particles are cemented 
and act as sand, which improves the mechanical 
condition of the soil. The physical action of lime 
upon soils is well illustrated in the case of 'loess soils,' 
which are composed of clay and limestone. The 
lime cements the clay particles and forms compound 
grains, making the soil more permeable, and more 
easily tilled. The improved physical condition alone 
which follows the application of lime fertilizers, is fre- 
quently sufficient to warrant their use. 

255. Application of Lime Fertilizers. — Lime is 
generally used as a top-dressing on grass lands at the 
rate of 200 to 500 pounds per acre. Excessive appli- 
cations are undesirable. Lime as gypsum is particu- 
larly valuable when applied to land where crops are 
grown which assimilate large amounts of lime. It 
should be remembered that it is not a complete, but 
mainly an indirect, fertilizer. 

If used to excess it may get the soil in such a con- 
dition that no more plant food can be rendered avail- 
able. A common saying is " Linie makes the father 
rich but the son poor."^' This is true, however, only 
when lime is used in excess. When used occasion- 
ally in connection with other manures, it has no inju- 
rious effects upon the soil and is a valuable fertil- 



202 SOILS AND FERTILIZERS 

izer, especially where clover is grown with difficulty. 
MISCELLANEOUS FERTILIZERS 

256. Salt is frequently used as an indirect fertilizer. 
Sodium and chlorine, the two elements of which it is 
composed, are not absolutely necessary for normal 
plant growth. When salt is applied to the soil and 
the sodium undergoes fixation, potassium may be 
liberated. An early experiment of Wolff illustrates 
this point : a buckwheat plot fertilized with salt pro- 
diiced a crop with more potash and less sodium than 
a similar unfertilized plot. 

Salt may be used to check the rank growth of straw 
during a rainy season, and thus prevent loss of the 
crop by lodging. It should not be used in excessive 
amounts, as it is destructive to vegetation ; 200 pounds 
per acre is a fair application. Salt also improves the 
physical condition of the soil by increasing the surface- 
tension of the soil water. Salt should not be used on 
a tobacco or potato crop, because it injures the quality 
of the product. 

257. Magnesium Salts. — Magnesium is present in 
the ash of all plants, and is an essential element of 
plant growth. Usually soils are so well stocked with 
this element that it is not necessary to apply it in 
fertilizers. Some of the magnesium salts, as the 
chloride, are injurious to vegetation, but when associa- 
ted with lime as carbonate, magnesia imparts fertility. 
In many of the Stassfurt salts magnesium is present. 



MISCELLANEOUS FERTILIZERS 203 

258. Soot. — The deposits formed in boilers and 
chimneys when wood and soft coal are burned contain 
small amounts of potash and phosphoric acid. They 
are valuable mainly as mechanical fertilizers impart- 
ing the properties of organic matter. There is but 
little plant food in soot, as shown by the following 
analysis : 

Soft-coal soot. Hard-wood soot. 

Per cent.i3 Per cent. 69 

Potash 0.84 1.78 

Phosphoric acid 0.75 0.96 

259. Seaweeds. — Seaweeds are rich in potash 
and near the sea coast are extensively used for fer- 
tilizers. 

Composition of 

nii.xed seaweed. 

Per cent 69 

Water 81.50 

Nitrogen 0.73 

Potash i_50 

Phosphoric acid o. 18 

260. Strand Plant Ash. — Weeds and plants pro- 
duced on waste land along the sea are in many Euro- 
pean countries burned, and the ashes used as fertilizer 
on other lands. By this means waste land is made to 
produce fertilizer for fields which are tillable. The 
amount of fertility removed in weeds is usuallv ofreater 
than that in agricultural plants, because weeds have a 
greater power of obtaining food from the soil. When 
wheat or other grain is raised, and a small crop of 
grain and a large crop of weeds are the result, there 
is more fertility removed from the soil than if a heavy 



204 SOILS AND FERTILIZERS 

stand of grain were obtained. The ashes of strand 
plants and weeds are extremely variable in composition. 
261. Wool Washings and Waste. — The washings 
from wool contain sufficient potash to make this 
material valuable as a fertilizer. In wool there is a 
high per cent, of potash, which is soluble, and readily 
removed in the washings. Wool waste may contain 
from I to 5 per cent, of potash and from 4 to 7 per 
cent, of nitrogen in somewhat inert forms. 



CHAPTER X 



COMMERCIAL FERTILIZERS AND THEIR USE 

262. Development of the Commercial Fertilizer 
Industry. — The commercial fertilizer industry owes 
its origin to Liebig's work on plant ash. The first 
superphosphate was made by Sir J. B. Lawes, about 
1840, from spent bone-black and sulphuric acid. His 
interest had previously been attracted to the use of 
bones by a gentleman who farmed near him, " who 
pointed out that on one farm bone was invaluable for 
the turnip crop, and on another farm it was useless. "^^ 
Since i860 the commercial fertilizer industry in this 
country has developed rapidly, until now the amount 
of money expended in purchasing commercial fer- 
tilizers and amendments is estimated at $60,000,000 
annually. Nearly all of this sum is expended in less 
than a quarter of the area of the United States. 

263. Complete Fertilizers and Amendments. — The 

term commercial fertilizer is applied to those materials 
which are made by the mixing of different substances 
which contain plant food in concentrated forms. 
When a commercial fertilizer contains nitrogen, phos- 
phoric acid, and potash, it is called a complete fer- 
tilizer, because it supplies the three elements which are 
liable to be most deficient. Materials as sodium nitrate 



206 SOILS AND FERTILIZERS 

which supply only one element are called amend- 
ments. It frequently happens that a soil requires only 
one element in order to produce good crops. In such 
cases only the one element needed should be sup- 
plied. Complete fertilizers are sometimes used when 
the soil is only in need of an amendment. 

264. Variable Composition of Commercial Fer- 
tilizers. — Since commercial fertilizers are made by 
mixing various materials which contain different 
amounts of nitrogen, phosphoric acid, and potash, it 
follows that they are extremely variable in composi- 
tion and value. No two samples are the same, 
hence the importance of knowing the com- 
position of every separate brand purchased. The 
composition of fertilizers is varied to meet the require- 
ments of different soils and crops. Some fertilizers 
are made rich in phosphoric acid, while others are 
rich in nitrogen and potash. 

265. How a Fertilizer is Made. — The most com- 
mon materials used in making complete fertilizers 
are : Nitrate of soda, kainit, and dissolved phosphate 
rock. These materials have about the following com- 
position : 

Nitrate of soda 15.5 per cent, nitrogen. 

Kainit 12.5 per cent, potash. 

Dissolved phosphate . . • 14.0 per cent, phosphoric acid. 

The fertilizer may be made rich or poor in any one 
element. Many fertilizers contain about twice as 



COMMERCIAL FERTILIZERS 207 

much potash as nitrogen and five times as much phos- 
phoric acid as potash. In order to make a ton of such 
a fertilizer it would be necessary to take about 

Pounds. 
Nitrate of soda 225 

Kainit 425 

Phosphate i , ro 

The ton of fertilizer would then contain about 35 
pounds of nitrogen, 189 pounds of phosphoric acid 
and 53 pounds of potash. These amounts are deter- 
mined by multiplying the percentage composition by 
the weight of material taken : 

Pounds. 

Nitrogen 225X0.155= 34.9 

Potash 425X0.125= 53.1 

Phosphoric acid 1350 X o. 14 = 189.0 

The fertilizer would then contain about 1.75 per 
cent, nitrogen, 2.65 percent, potash, and 9.45 percent, 
phosphoric acid. The percentage amounts are ob- 
tained by dividing the total pounds by 20. This fer- 
tilizer, if made at home from materials purchased in 
the market, would cost, exclusive of transportation and 
mixing, $18.79. 

Pounds. Cost. 

Nitrogen 34.9 (S> 14)4 cents = $5.06 

Phosphoric acid 189.0 (S. 6 cents = 11.34 

Potash 53-1 @ 4 >^ cents = 2.39 

Total $18.79 
A more concentrated fertilizer could be prepared 
by using high-grade sulphate of potash, superphos- 



208 SOILS AND FERTILIZERS 

phate, and ammonium sulphate. A fertilizer com- 
posed of these ingredients would contain : 

O 

*: T. ij 
Con 

Contanniig Total 'Z^'^ 

Pounds. percent. pounds. Value. Ph S'ii 

300 Sulphate of ammonia 20 N 60 @ 14}^ cents ^= $8.70 3.00 

500 Sulphate of potash. . 50 K.^O 250 @, 4>^ cents ^11.25 12.50 
1200 Superphosphate 35 P.fi^ 420 (a) 6 cents = 25,20 21.0 

Total $45.15 

So concentrated a fertilizer as the preceding is 
rarely, if ever, found on the market, although the 
price, $45.15 per ton, is frequently charged. This 
example is given to show the composition and trade 
value of one of the most concentrated fertilizers that 
could be produced. 

Any one of the different materials mentioned in the 
chapters on special fertilizers could be used, as dried 
blood, tankage, nitrate of soda, sulphate of ammonia, 
raw bone, dissolved bone, raw phosphate rock, dis- 
solved phosphate rock, basic slag, kainit, muriate or 
sulphate of potash, and many others. Inasmuch 
as each of these materials has a different value, it fol- 
lows that fertilizers, even of the same general com- 
position, may have widely different crop-producing 
powers. 

266. Inert Forms of Plant Food in Fertilizers. — 

A fertilizer of the same general composition as the first 



COMMERCIAL FERTILIZERS 209 

example could be made from feldspar rock, apatite 
rock, and leather. The leather contains nitrogen, 
the apatite contains phosphoric acid, and the feldspar, 
potash. Such a fertilizer would have no value when 
used on a crop, because all of the plant food elements 
are present in unavailable forms. Hence, in purchas- 
ing fertilizers, it is necessary to know not only the 
percentage composition, but also the nature of the 
materials from which the fertilizer was made. 

267. Inspection of Fertilizers. — In many states 
laws have been enacted regulating the manufacture 
and sale of commercial fertilizers, and provision is made 
for inspection and analysis of all brands offered for 
sale. The label on the fertilizer package must specify 
the percentage amounts of nitrogen, available phos- 
phoric acid and potash. Inspection has been found 
necessary in order to protect the farmer and the honest 
manufacturer. 

Occasionally a fraud is revealed like the following : 7° 

Natural plant food $25 to |28 per ton. 
Composition. Per cent. 

Total phosphoric acid 22.21 

Insoluble " " 20,81 

Available " " 1.40 

Potash soluble in water o. 13 

Actual value per ton, 1^:1.52. 

268. Mechanical Condition of Fertilizers. — When 
a fertilizer is purchased, the mechanical condition 
should also be considered. The finer the fer- 



2IO SOILS AND FERTILIZERS 

tilizer, as a rule, the better it is for promoting crop 
growth. Some combinations of plant food produce 
fertilizers which become so hard and lumpy that it is 
difficult to crush the lumps before spreading. The 
mass must be pulverized so as to be evenly distributed, 
otherwise the plant food will not be economically 
used. A fertilizer that passes through a sieve with 
holes 0.25 mm. in diameter is more valuable and can 
be used to better advantage than one of the same com- 
position that requires a 0.5 mm. sieve. 

269. Forms of Nitrogen in Commercial Fertilizers. 

— Nitrogen is present in commercial fertilizers in three 
forms : (i) Ammonium salts,(2) nitrates, and (3) organic 
nitrogen. The organic nitrogen is divided into two 
classes: (a) soluble in pepsin solution, and (d) insolu- 
ble in pepsin solution. The relative values of these 
different forms of nitrogen are discussed in Chapter 
IV. Three fertilizers may have the same amount of 
total nitrogen and still have entirely different crop- 
producing powers. 

. No. I. No. 2. No. ■!,. 

Nitrogen as : Per cent. Per cent. Per cent. 

Ammonium compounds ••• 1.75 0.25 o.io 

Nitrates 0.15 0.15 o. 10 

Organic nitrogen : 

Soluble in pepsin o. 10 1.25 0.55 

Insoluble in pepsin 0.35 1.25 

Total 2.00 2.00 2.00 

In purchasing fertilizers it is important to know not 
only the amount of nitrogen, but also the form in 



COMMERCIAL FERTILIZERS 211 

which it is present. In No. 3 the nitrogen is in inert 
forms like leather, while in No. 2 it is largely in the 
form of dried blood, and No. i has mainly ammonium 
compounds. Each of these fertilizers, as explained in 
the chapter on nitrogenous manures, has a different 
plant food value. 

270. Phosphoric Acid. — There are three forms of 
phosphoric acid in commercial fertilizers: (i) Water- 
soluble, (2) citrate-soluble, and (3) insoluble. The 
water- and citrate-soluble are called the available phos- 
phoric acid. In most fertilizers the phosphoric acid is 
derived from dissolved phosphate rock, and is in the 
form of monocalcium phosphate. The citrate-soluble 
is mainly dicalcium phosphate with variable amounts 
of iron and aluminum phosphates in easily soluble 
forms. The insoluble phosphoric acid is tricalcium 
and other phosphates which are soluble only in strong 
mineral acids. The insoluble phosphoric acid in fer- 
tilizers is considered as having but little value. As 
in the case of nitrogen three fertilizers may have the 
same total amount of phosphoric acid and yet have 
entirely different values. 

Water-soluble phosphoric acid. 
Citrate-soluble " " 

Insoluble " "' 

Total lo.co 10.00 10.00 

No. 3 is of but little value; the fertilizer contains in- 



No. I. 


No. 2. 


No. 3. 


!r cent. 


Per cent. 


Per cent. 


8.00 


0.25 


0.25 


1.50 


8.00 


0.75 


0.50 


1-75 


9.00 



212 SOII^S AND FKRTII.IZERS 

soluble phosphate rock or some material of the same 
nature. No. i is the most valuable, because it con- 
tains the least insoluble phosphoric acid. This fer- 
tilizer contains dissolved phosphate rock or dissolved 
bone. No. 2 is composed of such materials as the best 
grade of basic slag or roasted aluminum phosphate 
or fine steamed bone. 

271. Potash. — The three forms of potash in fer- 
tilizers are: (i) water-soluble, (2) acid-soluble, and (3) 
insoluble. Materials as sulphate of potash, kainit, and 
muriate of potash, which are soluble in water, be- 
long to the first class. In some states the fertilizer 
laws recognize only the water-soluble potash. In the 
second class are found materials like tobacco stems 
and the organic forms of potash. Substances like 
feldspar, which contain insoluble potash, are of no 
value in fertilizers. As a rule, the potash in commer- 
cial fertilizers is soluble in water; in only a few cases 
are acid-soluble forms met with. Insoluble potash 
would be considered an adulterant. 

272. Misleading Statements on Fertilizer Pack- 
ages. — Occasionally the percentage amounts of nitro- 
gen, phosphoric acid, and potash are' stated in mis- 
leading ways as ammonia, sulphate of potash, and 
bone phosphate of lime. Inasmuch as 14/17 of am- 
monia is nitrogen, the percentage figure for ammonia 
is proportionally greater than the nitrogen. And so 
with sulphate of potash which contains about 50 per 



COMMERCIAL FERTILIZERS 213 

cent, potash. This method of stating the composition 
can be considered in no other way than a fraud, 
especially when the fertilizer contains no sulphate of 
potash, but cheaper materials, and the phosphoric acid 
is not derived from bone. 

273. Estimated Commercial Value of Fertilizers, 

— The estimated value of a commercial fertilizer is 
obtained from the percentage composition and the 
trade value of the materials used. Suppose that two 
fertilizers are selling for $25 and $30, respectively, 
each having a different composition, the estimated 
values would be obtained in the following way : 

Composition of Fertii^izers. 

No. I. No. 2. 

Selling ptice $25. Selling price $30. 

Per cent. Per cent. 

Nitrogen as nitrates 1,50 2.10 

Phosphoric acid, available 8.00 10.00 

" " insoluble 2.00 0.50 

Potash { water-soluble) 2.00 3.50 

Pounds per Ton. 

No. I. No. 2. 

Nitrogen 1.50X20^ 30 2.10X20^= 42 

Phosphoric acid • 8.0 X 20 = 160 . lo.o X 20 = 200 
Potash 2.0 X 20 = 40 3.5 X 20 = 70 

Estimated Vai,ue. 

No. I. No. 2. 

Nitrogen 30 X o. 145 = $4.35 42 X o. 145 = $6.09 

Phosphoric acid 160 X 0-o6 = 9.60 200 X 0.06 = 12.00 

Potash 40 X 0-045 = i-8o 70 X 0.045 = 3- 15 

$15.75 I21.24 



214 



SOILS AND FERTILIZERS 



Difference between estimated vahie and selling 
price, No. i, $9.25; No. 2, $8.76. 

274. Home Mixing. — At the New Jersey Experi- 
ment Station it has been shown that " the charges of 
the mannfactnrers and dealers for mixing, bagging, 
shipping, and other expenses are on the average $8.50 
per ton, and also that the average mannfactured fer- 
tilizer contains abont 300 ponnds of actnal fertilizing 
constituents per ton. These figures are practically 




< ^i 



Fig. 34. Composition of Fertilizers. 

true of other states where large quantities of commer- 
cial fertilizers are used.''^^ in states where smaller 
amounts are used the difference between the estimated 
cost and selling price is greater than $8.50. 

These facts emphasize the economy of home mixing. 
The difference in price between the raw materials 
and the product sold is frequently so great that it is an 
advantage for the farmer to piirchase the raw mate- 
rials, as sulphate of potash, nitrate of soda, and acid 



COMMERCIAL FERTILIZERS 215 

phosphate, and mix them as desired. By so doing a 
fertilizer of any composition may be prepared and 
there is less danger of securing an inferior article. 
Of course it is not possible by means of shovels and 
sieves to accomplish as thorough mixing of the ingre- 
dients as with machiner}'. 

o 

cC.Ti '-' 

Formula No. i. ^E.15 

Pounds. Pounds, e, S^ 

Nitrate of soda 500 containing nitrogen 77.5 3.87 

Acid phosphate 1200 containing phos. acid--. 16S.0 8.40 

Sulphate of potash • . 300 containing potash 150.0 7.50 



Total r.' 395.5 

Formula No. 2. 

Nitrate of soda 250 containing nitrogen 38.7 i .99 

Acid phosphate 900 containing phos. acid... 126.0 6.3 

Sulphate of potash . . 450 containing potash 225.0 11. 5 

Plaster, etc 400 



Total 389. 7 

Formula No. 3. 

Nitrate of soda 200 containing nitrogen 31.0 1.55 

Acid phosphate 1500 containing phos. acid..- 210.0 10.50 

Sulphate of potash . . 150 containing potash 75.0 5.75 

Plaster, etc 150 



Total 316.0 

275. Fertilizers and Tillage. — Commercial fer- 
tilizers cannot be made to take the place of good 
tillage, which is equally as important when fertilizers 



2l6 SOILS AND FERTILIZERS 

are used as when they are omitted. Scant crops are 
as frequently due to the want of proper tillage as to 
the absence of plant food. Poor cultivation results in 
getting the soil out of condition ; then instead of thor- 
oughly preparing the land, commercial fertilizers are 
resorted to, and the conclusion is reached that the soil 
is exhausted, when in reality it is suffering for the want 
of cultivation, for a dressing of land plaster, for farm 
manures, or for a change of crops. There is no ques- 
tion but what better tillage, better care and use of 
farm manures, the culture of clover and the systematic 
rotation of crops would result in greatly reducing the 
$60,000,000 annually spent for commercial fertilizers, 
without reducing the yield of crops. The better the 
cultivation, the less the amount of commercial fer- 
tilizer required. 

276. Abuse of Commercial Fertilizers. — When a 
soil produces poor crops, a complete fertilizer is fre- 
quently used when an amendment only is needed. 
Restricted crop production in long cultivated soils is 
due to deficiency of available nitrogen. If the nitro- 
gen were supplied, improved cultivation would gen- 
erally furnish the available potash and phosphoric 
acid, but instead of providing the one element needed, 
others which may already be present in the soil in 
liberal amounts, are often supplied at a great expense. 
Another abuse of fertilizers is their application to the 
wrong crop. A heavy application of potash fertilizer 



FIELD TESTS WITH FERTILIZERS 217 

to a wheat crop grown on a clay soil, or an application 
of nitrate of soda on land seeded to clover, or of land 
plaster to flax grown on a limestone soil, w^ould be a 
useless w^aste of money. 

277. Proper Use of Fertilizers. — In order to make 
the best use of commercial fertilizers, both the soil and 
the crop must be carefully considered. All crops do 
not possess the same power of obtaining food from the 
soil ; turnips, for example, have very restricted powers 
of phosphate assimilation, hence they require special 
manuring with })hosphates. Wheat requires help in 
obtaining its nitrogen. A wheat crop will starv^e for 
the want of nitrogen, while an adjoining corn crop will 
scarcely feel its need. Wheat has strong power of 
assimilating potash compounds, w^hile clover has less. 
Hence in the proper use of fertilizers the power of the 
plant to obtain its food must be considered. An 
application of potash to clover, nitrogen to wheat, and 
phosphoric acid to turnips, would be a judicious use of 
these fertilizers, while if a mixture of the three ele- 
ments were applied to each crop alike, the clover 
w^ould not be particularly benefited by the nitrogen 
or the wheat by the potash. Before commercial fertili- 
zers are used, careful field trials should be made with 
different crops. 

FIELD TESTS WITH FERTILIZERS 

278. Experimental Plots. — A piece of land w^ell 



2l8 SOILS AND FERTILIZERS 

tilled and of uniform texture, should be used for field 
trials with fertilizers. After preparation for the crop, 
small plots, 1/20 of an acre, are staked off. A con- 
venient size is, length 204 feet, width 10 feet 8 inches, 
area 2176 square feet. Between each plot a strip 3 
feet wide should be left. In these experiments the 
plan is to apply one element or a combination of 
elements to a plot and compare the results with other 
•plots treated differently.^^ 

279. Preliminary Trials. — It is best to make pre- 
liminary trials one year and verify the conclusions the 
next. In making the tests the first year eight plots 
are necessary and fertilizers are applied in the follow- 
ing way : 

The first plot receives no fertilizer and is used as the 
basis for comparison. 

The second plot receives a dressing of 8 pounds of 
nitrate of soda, 16 pounds acid }>hosphate, and 8 
pounds sulphate or muriate of potash. 

The third plot receives nitrogen and phosphoric 
acid. 

The fourth plot receives nitrogen and potash. 

The fifth plot receives nitrogen. 

The sixth plot receives phosphoric acid and potash. 

The seventh plot receives potash. 

The eighth plot receives phosphoric acid. 



FIELD TESTS WITH FERTILIZERS 



219 



No fertilizer. 
I. 


N 
P.O5 
K,0 

2. 


N 
P.O5 

v3- 


N 
K,0 

4. 




N 
5- 


P.O5 
K,0 

6. 


K,0 

7- 


P.O5 

8. 



Should good results be obtained on plot No. 3, the 
indications are that there is a deficiency of the two 
elements nitrogen and phosphoric acid. An increased 
yield from No. 4 indicates deficiency of nitrogen and 
potash. Under such conditions the use of a complete 
fertilizer would be unnecessary. If No. 5 gives an 
additional yield the soil is in want of nitrogen. From 
the eight plots it will be possible to tell which of the 
various elements it will be advisable to use. The fer- 
tilizers should be applied after the land has been thor- 
oughly prepared and before seeding. Corn is a good 
crop for the first trials. The number of plots may be 
increased by using well-prepared stable manure and 
gypsum on plots 9 and 10 respectively. The second 
year the results should be verified. 

280. Deficiency of Nitrogen. — If the results indi- 
cate a deficiency of nitrogen, select two crops, one as 
wheat which is particularly benefited by dressings of 
nitrogen, and another as corn which has no difficulty in 
obtaining this element. The cultivation of each crop 
should be that which experience has shown to be the 



220 SOILS AND FERTILIZERS 

best. On one wheat, and one corn plot, 8 ponnds of 
nitrate of soda shonld be used, a plot each of wheat 
and corn being left nnfertilized. If both the corn and 
the wheat are benefited by the application of nitro- 
gen, the soil is in need of available nitrogen. If, how- 
ever, the wheat responds and the corn does not, the 
soil is not in great need of nitrogen but does not con- 
tain an abundance in available forms. 

281. Deficiency of Phosphoric Acid. — In experi- 
menting with phosphoric acid, turnips are grown on 
two plots and barley on two plots. To one plot of 
each 16 pounds of acid phosphate are applied. If both 
crops show marked additional yields the soil is in need 
of available phosphoric acid. If only the turnips re- 
spond while the barley is indifferent the soil contains 
a fair amount of available phosphoric acid. Barley 
and turnips are used because there is such a marked 
difference in the power of each to assimilate phos- 
phoric acid. 

282, Deficiency of Potash. — In order to determine 
the condition of the soil as to potash, potatoes and oats 
may be used as the trial crops, and 8 pounds of sul- 
phate of potash should be applied to one plot of each. 
Marked additional yields indicate a poverty of availa- 
ble potash ; an increased potato crop and an indiffer- 
ent oat crop indicate potash not in the most available 
forms. If no additional yields are obtained the soil 
is not in need of potash. 



FIELD TESTS WITH FERTILIZERS 22 1 

283. Deficiency of Two Elements. — If the prelim- 
inary trials indicate a deficiency of two elements as 
nitrogen and phosphoric acid, both elements are used 
together, in the same way as described for deficiency 
of nitrogen, with additional plots for the separate ap- 
plication of nitrogen and phosphoric acid. 

284. Importance of Field Trials. — While it seems a 
troublesome matter to determine the actual needs of a 
soil, it W'ill be found that both time and money are 
saved by a systematic study of the question. Suppose 
fertilizers are used in a " hit or miss" w^ay year after 
year on a soil, deficient only in phosphoric acid. It 
would take 8 years to find out what the soil w^as 
deficient in, if a different fertilizer were used each year, 
and during all this period, either the soil has failed to 
receive its proper fertilizer, or expensive and unneces- 
sary plant food has been provided. 

285. Will it Pay to Use Commercial Fertilizers? 
— This question can be answered only by trial. If a 
soil is in need of available plant food, the additional 
amount of crop produced should pay for the fertilizer 
and the expense of using it. Some fertilizers have an 
influence on two or three succeeding crops, and only 
partial returns are received the first year. When large 
crops must be produced on small areas, as in truck 
farming, commercial fertilizers are generally neces- 
sary. In the production of large areas of staple crops 
as wheat and corn, in the western prairie states, 



222 SOILS AND FERTILIZERS 

they have never been used. If the soil is properly 
tilled and there is a good stock of natural fertility, the 
use of commercial fertilizers can be avoided. With 
poor cultivation and a soil that has been impoverished 
by injudicious cultivation their use is more necessary. 

286. Amount of Fertilizer to Use per Acre. — When 
commercial fertilizers are used, it should be the aim to 
apply just enough to produce normal yields. Heavy 
applications at long intervals are not as productive of 
good results as light applications more frequently. 
From 400 to 600 pounds per acre is as much as should 
be used at one time unless previous trials have shown 
that heavier applications are necessary. The way in 
which the fertilizer is to be applied, as broadcast or 
otherwise, must be determined by the crop to be 
grown. The fertilizer should not come in direct con- 
tact with seeds, neither should it be worked into the 
soil to such a depth that it may be lost by leaching 
before it can be appropriated by the crop. 

287. Excessive Applications of Fertilizers Injuri- 
ous. — An overabundance of plant food has an inju- 
rious effect upon crop growth. Plants take their 
food from the soil in dilute solutions, and when 
the solution is concentrated abnormal growth results. 
Potatoes heavily manured with nitrate of soda make a 
luxuriant growth of vines but produce only a few 
small tubers. When a medium dressing is used along 
with potash and phosphoric acid, a more balanced 



FIELD TESTS WITH FERTILIZERS 223 

growth is obtained, and a better yield is the result. 
Heavy applications of nitrate of soda produce a rank 
growth of straw, with a low yield of grain. The ex- 
cessive amount of nitrogen causes the mineral matter 
to be utilized for straw production and leaves only a 
small amount for grain production. When applica- 
tions of commercial fertilizers are too heavy, plants 
take up unnecessary amounts of food and fail to make 
good use of it. In fact crops may be overfed the 
same as animals. Hence in the use of fertilizers ex- 
cessive applications are to be avoided. 

288. Fertilizing Special Crops. — There are crops 
which need special help in obtaining some one ele- 
ment, and in the use of fertilizers it should be the rule 
to help those crops which have the greatest difficulty 
in obtaining^ food. When the soil does not show a 
marked deficiency in any one element, light dressings 
of special purpose manures may be made to the follow- 
ing crops : 

Wheat. — Nitrogen first; phosphoric acid to a less 
extent. 

Barley^ oats^ and rye require manuring like wheat, 
but to a less extent. Each crop has a different power 
of obtaining nitrogen. Wheat requires the most help 
and barley and rye the least. 

■ Corn. — Phosphoric acid first ; then nitrogen and 
potash. 



224 SOILS AND FERTILIZERS 

Potatoes. — General manuring ; reenforced with pot- 
ash. 

Mangels. — Nitrogen. 
Turnips. — Phosphoric acid. 
Clover. — Lime and potash. 
Timothy. — General manuring. 

289. Commercial Fertilizers and Farm Manures. 

— Commercial fertilizers should not replace farm ma- 
nures, but simply reenforce them. Although com- 
mercial fertilizers are called complete manures, they 
fail to supply organic matter. It is more important in 
some soils than in others, that the organic matter be 
maintained because in some soils the organic matter 
takes a more important part in crop production than 
does the food applied in commercial forms. For 
example, when a rich prairie soil is reduced by grain 
cropping and is allowed to return to pasture, heavier 
yields of grain are afterwards obtained than from sim- 
ilar soils which received applications of commercial 
fertilizers. 



CHAPTER XI 

FOOD REQUIREMENTS OF CROPS 

290. Amount of Fertility Removed by Crops. — 

From an acre of soil, producing average crops, the 
amount of fertility removed varies between wide lim- 
its. For example, an acre of mangels removes 150 
pounds of potash, while an acre of flax removes 27 
pounds ; an acre of corn removes about 75 pounds of 
nitrogen, while an acre of wheat removes about 35 
pounds. Crops which remove the most fertility do 
not always require the most help in obtaining their food. 
This is because the amount of plant food assimilated, 
and the power of crops to obtain this food, are not 
the same. An acre of corn, for example, takes over 
twice as much nitrogen as an acre of wheat, but wheat 
will often leave the soil in a more impoverished con- 
dition than corn, because corn has greater powder for 
procuring nitrogen and for utilizing that formed by 
nitrification after the wheat crop has completed its 
growth. The available nitrogen if not utilized by a 
crop may be lost in various ways. Mangels require 
about twice as much phosphoric acid as flax, but are 
a strong feeding crop and require less help in obtain- 
ing this element. 

It was formerly believed that the amount of plant 



226 SOILS AND FERTILIZERS 

food present in the matured crop indicated the kind 
and amount of fertilizing ingredients to apply, and 
that a correct system of manuring required a return 
to the soil of all elements removed in the crop. Ex- 
periments have shown that both of these views are in- 
correct. The composition of plants cannot be taken as 
the basis for their inanuring. For example an acre of 
wheat contains 35 pounds of nitrogen while an acre of 
clover contains 70 pounds. If 70 pounds of nitrogen 
were applied to an acre of clover and 35 pounds to an 
acre of wheat, poor results would follow, because clo- 
ver can obtain its own nitrogen while wheat is nearly 
helpless in obtaining it, and the 35 pounds would not 
necessarih' come in contact with the roots so that it 
could all be assimilated. While the amount of plant 
food removed in crops cannot serve as the basis for their 
manuring, valuable results are obtained from the study 
of the different elements of fertility removed in crops, 
and in making use of the following figures, other fac- 
tors, as the influence of the crop upon the soil and the 
power of the crop to obtain its food, must also be con- 
sidered. 



FOOD REQUIREMENTS OF CROPS 227 

PI.ANT Food Removed by Crops" 

Pounds per acre. 
Phos- 
Gross Nitro- phoric Pot- Sil- Total 

Crops. weight. gen. acid. ash. Lime. ica. ash. 

Wheat, 20 bus 1200 25 12.5 7 i i 25 

Straw 2000 10 7.5 28 7 115 185 

Total 35 20 35 8 116 210 

Barley, 40 bus 1920 28 15 81 12 40 

Straw 3000 12 5 30 8 60 176 

Total 40 20 38 9 72 216 

Oats, 50 bus 1600 35 12 10 1.5 15 55 

Straw 3000 15 6 35 9.5 60 150 

Total 50 18 45 II. o 75 205 

Corn, 65 bus 2200 40 18 15 i i 40 

Stalks 3000 35 2 45 II 89 160 

Total 75 20 60 12 90 200 

Peas, 30 bus 1800 .. 18 22 4 i 64 

Straw 3500 .. 7 38 71 9 176 

Total 25 60 75 10 240 

Mangels, 10 tons.. 20000 75 35 150 30 10 350 

Meadow hay, i ton 2000 30 20 45 12 50 175 

Red Clover Hay, 

2 tons 4000 .. 28 66 75 15 250 

Potatoes, 150 bus. . 9000 40 20 75 25 4 125 

Flax, 15 bus 900 39 15 8 3 0.5 34 

Straw 1800 15 3 19 13 3 53 

Total 54 18 27 16 3.5 87 

291. Plants Render Their Own Food Soluble. — It 

was supposed at one time that plants obtained all of 
their mineral food from the mineral matter dissolved 
in the soil water. Experiments by Liebig demonstra- 
ted that plants have the power of rendering their own 
food soluble, provided it does not exist in forms 



228 SOILS AND FERTILIZERS 

too inert to undergo chemical change. Iviebig grew 
barley in boxes so constructed that all of the water- 
soluble plant food could be secured. Two of the boxes 
were manured and two left unmanured. In one box 
which received manure and one which received none, 
barley was grown. One each of the manured and 
unmanured boxes was left barren. He collected all of 
the drain waters and determined the soluble mineral 
matter present, also weighed and analyzed the crop. 
His results showed that 92 per cent, of the potash in 
the crop was obtained from forms insoluble in water. ^^ 

In the roots of all plants there are present various 
organic acids. Between the rootlet and the soil there 
is a layer of water. The plant sap and the soil water 
are separated by plant tissue which acts as a membrane. 
All of the conditions are favorable for osmosis. The 
acid sap from the roots finds its way into the soil in 
exchange for some of the soil water. This acid, excre- 
ted by the roots, acts upon the mineral matter, render- 
ing it soluble, when it is taken up by the plant. 
Different plants contain different kinds and amounts 
of organic acids as well as present different areas of 
root surface to act upon the soil, and the result is that 
agricultural crops have different powers of assimila- 
ting food. 

Plants not only possess the power of rendering their 
food soluble but they are also able to select their own 
food and to reject that which is unnecessary. For ex- 



CEREAL CROPS 229 

ample, wheat grown on prairie soil containing soda in 
equally abundant and soluble forms as the potash, will 
contain relatively little soda compared with the potash 
in the crop.^^ 

CEREAL CROPS 

292. General Food Requirements. — Cereal crops con- 
tain a high per cent, of silica and evidently possess 
the power of feeding upon some of the simpler silicates 
of the soil, 73 liberating the base elements which are 
utilized as food, while the silica is deposited in the 
outer surface of the straw. As previously stated, cer- 
eal crops although they do not remove large amounts 
of total nitrogen from the soil require special help in 
obtaining this element. There is, however, a great 
difference among the cereals as to power of assimila- 
ting nitrogen. Next to nitrogen these crops stand 
most in need of phosphoric acid. The humic phos- 
phates are utilized by nearly all of the cereals. 

293. Wheat. — This crop is more exacting in its 
food requirements than barley, oats, or rye. Wheat 
is comparatively a weak feeding crop, and the 
soil should be in a higher state of fertility than for 
other grains. The extensive experiments of Lawes 
and Gilbert have given valuable information regard- 
ing the effects of manures on wheat. The results are 
given in the following table 'J^ 



230 SOILS AND FERTILIZERS 

Average Yield of Wheat per Acre. 

Bushels. 

No manure for 40 years 14 

Minerals alone for 32 years 15I- 

Nitrogen " " " " 23I 

Farmyard manure for 32 years 32I 

Minerals and nitrogen for 32 years' 36|^ 



2 -, 9 3 



The food requirements of wheat are such that it should 
be given a favored position in the rotation. Wheat may 
follow clover provided the clover sod is light and is 
fall plowed. On some soils, however, wheat does not 
thrive following a sod crop. It takes nearly a year 
for a heavy sod residue to get into suitable food forms 
for a wheat crop. Under such conditions, oats should 
first be sown, then wheat may follow. On average 
soil a medium clover sod, plowed late in summer or in 
early fall, and followed wath surface cultivation, leaves 
the land in good condition for spring wheat. It is not 
advisable to have wheat follow barlev, because the 
soil will be too porous, and barley being a stronger 
feeding crop leaves the land in poor condition as to 
available plant food. When a corn crop is well ma- 
nured, wheat may follow. The food requirements of 
wheat are best satisfied following a light, well cultiva- 
ted clover sod, or following oats which have been grown 
on heavy sod, or following corn that has been well 
manured. 

1 86 pounds of nitrogen as sodium nitrate. 

2 86 " " " " ammouium salts. 



CEREAL CROPS 23I 

294. Barley. — While wheat and barley belong to 
the same general class of cereals, they differ greatly in 
their habits and food requirements. Barley is a 
stronger feeding crop, has a greater root development 
near the surface, and can utilize food in cruder forms. 
In many of the western states, soils wdiich produce 
poor wheat crops, from too long cultivation, give ex- 
cellent yields of barley. This is due to changed con- 
ditions, of both the chemical and mechanical composi- 
tion of the soil. Long cultivation has made the soil 
porous and reduced the nitrogen content. Barley 
thrives best on a rather open soil and has greater ni- 
trogen assimilative powers than wheat. Barley, how^- 
ever, responds liberally to manuring, particularly to ni- 
trogenous manures. The experiments of Lawes and 
Gilbert on the growth of barley are briefly summa- 
rized in the following tablets 

Average Yield of Barlev Per Acre for 34 Years. 

Bushels. 

No manure 1 7| 

Superphosphate alone 23I 

Mixed minerals 24! 

Nitrogen alone • • • • 3o| 

Nitrogen and superphosphate 45 

Farmyard manures 49.J 

295. Oats. — Oats are capable of obtaining food un- 
der more adverse conditions than either barley or 
wheat. They are also less exacting as to soil require- 
ments. The oat plant will adapt itself to either sandy 



232 SOILS AND FERTILIZERS 

or clay soil, and will thrive in the presence of alkaline 
matter or huniic acid where wheat would be destroyed. 
In a rotation, oats usually occupy a position less favored 
by manures. They are, however, greatly benefited by 
fertilizers particularly by those of a nitrogenous na- 
ture. 

296. Corn. — Experiments with corn indicate that 
under ordinary conditions it requires most help in ob- 
taining phosphoric acid. Corn removes a large amount 
of gross fertility but its habits of growth are such that 
it generally leaves an average soil in better condition 
for succeeding crops. Corn is not injured as are many 
grain crops by heavy applications of stable manure. 
It does not, like flax, produce waste products which 
are destructive to itself. Rich prairie soils when 
newly broken give better results for wheat culture 
after one or two corn crops have been removed. The 
food requirements of corn are satisfied by applications 
of stable manure, occasionally reenforced with a little 
phosphoric acid. After clover, corn gives excellent 
returns, and when corn is the chief market crop it 
should be favored by having the best position in a ro- 
tation. 

MISCELLANEOUS CROPS 

297. Flax is very exacting in food requirements 
and for its culture the soil must be in a high state of 
fertility. It is a type of a weak feeding crop. There 
are but few roots near the surface and consequently it 



MISCELLANEOUS CROPS 233 

has restricted powers of nitrogen assimilation.37 Flax 
does not remove a large amount of fertility but if 
grown too frequently the tendency is to get the land 
out of condition rather than to exhaust it. Flax 
should be indirectly manured. Direct applications of 
stable manure produce poor results, but when the ma- 
nure is applied to the preceding crop excellent results 
are obtained. The best conditions for flax culture re- 
quire that it should be grown on the same land only 
once in five years. Dr. Lugger has demonstrated 
that there are produced, when the roots and straw of 
flax decay, products which are destructive to succeed- 
ing flax crops. 7^ The food requirements of flax are 
met when it follows corn which has been well manured, 
or a sod which has been given the cultivation described 
for wheat. Flax and spring wheat are much alike in 
food requirements. 

298. Potatoes. — Potatoes are surface feeders and 
when grown continually upon the same soil without 
manure, the yield per acre decreases more rapidly than 
any other farm crop. Experiments with potatoes by 
Lawes and Gilbert using different manures gave the 
following result 'J'' 

Average Yield per Acre for 12 Years. 

Tons. Cwt. 

No manure i 19I 

Superphosphate 3 5 

Minerals alone 3 7| 

Nitrate of soda alone 2 4| 

Mixed manures and nitrogen 5 17I 

Farm manures, alternate years 4 3| 



234 SOILS AND FERTILIZERS 

Potatoes require liberal general manuring reenforced 
with wood ashes or other potash fertilizers. In the 
rotation they should follow grain or pasture land, pro- 
vided the fertility of the soil is kept up. 

299. Sugar-beets. — This crop is more exacting in 
its food demands than other root crop. Excessive 
fertility is not conducive to a high content of sugar. 
Soils in a medium state of fertility usually give the 
best results. 7^ Sugar-beets should not receive heavy 
dressings of stable manure, because an abnormal 
growth results. Nitrogenous fertilizers can be ap- 
plied only in limited amounts, heavier dressings of 
potash and phosphoric acid are more admissible. 
When sugar-beets follow corn which has been manured, 
or grain which has left the soil in an average state of 
fertility, the food requirements are well met. 

300. Roots. — Mangels are gross feeders and re- 
move a larger amount of fertility from the soil than 
any other farm crop.73 When fed to stock and the 
manure is returned to the soil they materially aid in 
making the plant food more available for delicate 
feeding crops. Mangels are better able to obtain their 
phosphoric acid than are turnips and need the most 
help in the way of nitrogen. Turnips are surface 
feeders with stronger power of nitrogen assimilation 
than the grains but with restricted power of phosphate 
assimilation. Manures for turnips should be phos- 
phatic in nature. . 



MISCELLANEOUS CROPS 235 

301. Rape is a type of a strong feeding plant capa- 
ble of obtaining its food nnder conditions adverse to 
grain cnlture. When grown too frequently upon the 
same soil it does not thrive. On account of its great 
capacity for obtaining food, it is a valuable crop to 
use for green manuring purposes. ^9 

302. Buckwheat is a strong feeding crop and its 
demands for food are easily met. On rich soil, a rank 
growth of straw results, with poor seed formation. 
Buckwheat is usually sown upon the poorest soil of 
the farm. Being a strong feeder it is frequently used 
as a manurial crop, being plowed under while green to 
serve as food for weaker feeding crops. 

303. Cotton. — On average soils cotton stands in 
need first of phosphoric acid, second of nitrogen.^° It 
is most able to obtain potash, but soils deficient in pot- 
ash require its use. Organic nitrogen as cottonseed 
meal and stable manure appear equally as effective as 
nitric nitrogen. Phosphoric acid must be applied in 
the most available forms. In fertilizing cotton, 
the use of green manuring crops as cow peas with an 
application of marl gives beneficial results. Marl, how- 
ever, should not be applied alone because of the forma- 
tion of insoluble phosphate of lime. Lime combines 
with the decaying organic matter in preference to 
phosphates, a result which is beneficial to both soil 
and crop. 

304. Hops. — The hop plant is peculiar in regard 



236 SOILS AND FERTILIZERS 

to its food requirements. An excess of easily soluble 
plant food is injurious while a lack is equally so. An 
abundance of food in organic forms is most essential. 
Heavy dressings of farm manures may be applied. 
Where hops are grown there is a tendency to use all 
of the manure on the hops while the rest of the farm 
is left unmanured. Very light applications of com- 
mercial fertilizers may be used in connection with sta- 
ble manure, but such use should be made only after a 
preliminary trial on a smaller scale. 

305. Hay and Grass Crops. — Most grass crops have 
shorter roots than grain crops ; they are surface feed- 
ers and not so able to secure mineral food. When a 
number of crops have been removed the soil may stand 
in need of available mineral matter. Farm manures 
are particularly well adapted for fertilizing grass. • Ap- 
plications of nitrogenous manures result in discoura- 
ging the growth of clover. Heavy manuring of grass 
land has a tendency to reduce the number of species 
and one kind is apt to predominate.^' On some soils 
ashes, and on others lime fertilizers, have been found 
ver}' beneficial. The manuring of grass lands must 
be varied to meet the requirements of different soils. 
Permanent meadows require different manuring from 
meadow simply introduced as an important crop in the 
rotation. 

306. Leguminous Crops. — For leguminous crops pot- 
ash and lime fertilizers have been found of most value. 



MISCELLANEOUS CROPS 237 

Analyses of leguminous crops, as clover and peas, show 
large amounts of both potash and lime. Many crops 
as clover fail when grown too frequently upon the 
same soil, not because the soil is exhausted but because 
of the development in the soil of organic products 
which are destructive to growth. When the inexpen- 
sive food requirements of leguminous crops are sup- 
plied, the soil is enriched with nitrogen and phos- 
phoric acid which have been changed to more availa- 
ble forms. 



CHAPTER XII 

ROTATION OF CROPS AND CONSERVATION OF SOIL 
FERTILITY 

307. Object of Crop Rotation. — The object of the 
systematic rotation of crops is to conserve the fertility 
of the soil, and at the same time to produce larger 
yields. In order to accomplish this, the food require- 
ments of different crops must be met by good cultiva- 
tion and proper manuring. Rotations must be planned 
according to the nature of the soil and the system of 
farming that is to be followed. For general grain 
farming a different system must be practiced than for 
exclusive dairying. Whatever the nature of farming 
the whole farm should gradually undergo a s}'stematic 
rotation. If the farm is uneven in soil texture, differ- 
ent rotations must be practiced on the various parts. 
There is no way in which soils are more rapidly de- 
pleted of fertility than by the continued culture of one 
crop. In exclusive wheat raising for example the 
losses which occur are not confined to the fertility re- 
moved in the crop but may take place in other ways 
as described in the chapter on nitrogen. When wheat 
is properly grown in alternation with other crops, 
losses of nitrogen are reduced to the minimum. 

When remunerative crops can no longer be produced 
the soil is said to be exhausted. Soil exhaustion may 



ROTATION OF CROPS 239 

be due either to a lack of fertility or to o^ettino- the 
soil out of condition because of the "one-crop system" 
and poor methods of cultivation. 

308. Principles Involved in Crop Rotation. — In 
the systematic rotation of crops there are a few funda- 
mental principles with which all rotations should be 
made to conform. Briefly stated these principles are : 

1. Deep and shallow rooted crops should alternate. 

2. Humus-consuming and humus-producing crops 
should alternate. 

3. Crops should be rotated so as to make the best 
use of the preceding crop residue. 

4. Crops should be rotated so as to secure nitrogen 
indirectly from atmospheric sources. 

5. Crops should be rotated so as to keep the soil in 
the best mechanical condition. 

6. In arid regions crops should be rotated so as to 
make the best use of the soil water. 

7. An even distribution of farm labor should be se- 
cured by a rotation. 

8. Farm manures and fertilizers should be used in 
the rotation where thev will do the most eood. 

9. Rotations should be planned so as to produce fod- 
der for stock, and so that every year there will be some 
important crop to be sold. 

309. Deep and Shallow Rooted Crops. — When 
deep and shallow rooted crops alternate, the draft upon 
the surface soil and subsoil is more evenlv distributed. 



240 SOILS AND FERTILIZERS 

In many soils nitrogen and phosphoric acid are more 
abundant in the surface soil while potash and lime 
predominate in the subsoil. When such a condition 
exists, the alternating of deep and shallow rooted 
crops is very beneficial, because the surface soil is re- 
lieved of continuous heavy drafts upon the elements 
present in scant amounts. 

310. Humus-consuming and Humus-producing 
Crops. — When grain or hoed crops are grown con- 
tinuously, oxidation of the humus occurs, and the 
chemical and physical properties of the soil may be 
entirely changed by the loss of the humus. The ro- 
tating of grass and grain crops and the use of stable 
manure serve to maintain the humus equilibrium. On 
some soils lime may be required along with the humus 
to prevent the formation of humic acid, and in such 
cases the best conditions exist when both lime and hu- 
mus materials are supplied. The alternation of hu- 
mus-producing and humus-consuming crops is one of 
the essential matters to consider in a rotation. 

311. Crop Residue. — Crop residues should always 
be placed at the disposal of weak feeding crops. For 
example, after a light clover and timothy sod, wheat 
or flax should be grown in preference to barley or 
mangels. The weak feeding crop should then be fol- 
lowed by a strong feeding crop, and each is properly 
supplied with food. It would be poor economy, on an 
average soil, to follow clover and timothy with mangels, 



ROTATION OF CROPS 24 1 

then with barley, and finally with flax, because the 
flax would be placed at a serious disadvantage follow- 
ing two strong feeding crops. If reversed, the crops 
would be placed in order of assimilative power, and the 
best use would be made of the sod crop residue. 
When crops of dissimilar feeding habits follow each 
other in rotation not only are the crop residues used to 
the best advantage, but the soil is relieved of excessive 
demands on special elements. For example, wheat 
and clover take different amounts of potash and lime 
from the soil. Wheat has the power of feeding upon 
silicates of potash which clover cannot assimilate, 
hence wheat and clover in rotation relieve the soil of 
excessive demands on the potash. 

312. Nitrogen-consuming and Nitrogen-producing 
Crops. — It is possible in a five-course rotation to main- 
tain or even increase the nitrogen of the soil without 
the use of nitrogenous manures. In Section 131 an ex- 
ample is given of a rotation which has left the 
soil with a better supply of nitrogen than at the begin- 
ning. When a soil produces a good clover crop once 
in five years, and stable manure is used once during 
the rotation, the soil nitrogen is not decreased. By 
means of rotating nitrogen-producing and nitrogen- 
consuming crops it is possible to sell nitrogenous grain 
products from the farm without purchasing nitroge- 
nous manures. The conservation of the nitrogen of 
the soil is the most important point to consider in the 



242 SOILS AND FERTILIZERS 

rotation of crops, because it is the most expensive ele- 
ment and is the most liable to be deficient. 

313. Influence of Rotation upon the Mechanical 
Condition of Soils. — With different kinds of crops, 
the mechanical conditions of soils are constantly under- 
going change. Grain crops and hoed crops tend to 
make the soil open in texture. Grass crops have the 
opposite effect. All soils should undergo periodic 
compacting and loosening. Some require more of one 
treatment than of the other. In a good rotation the 
mechanical action of the crop upon the soil should be 
considered, otherwise the soil may get into poor condi- 
tion to . retain water or become so loose that heavy 
losses occur through wind storms. Sandy soils are 
improved by those methods of cropping which compact 
the soil, while heavy clays require the opposite treat- 
ment. The rotation should be made to conform to 
the requirements of the soil. 

314. Economic Use of Soil Water. — The rotation 
should not be of such a nature as to make excessive 
demands upon the soil water. For example, after a 
grain crop has been produced, it is best in regions of 
scant rainfall to plow the land and get it into condi- 
tion to conserve the water for the next year's crop, 
rather than to attempt to raise a catch crop the same 
year. Crops removing excessive amounts of water 
should not be grown too frequently. Sunflowers, for 
example, remove twenty times more water than grain 



ROTATION OF CROPS 243 

crops. Cabbage removes from the soil more water 
than mail}' other crops. With a good rotation it is 
possible to carr}' the water balance in the soil from 
year to year, so that crops will be snpplied in times of 
drought. 

315. Rotation and Farm Labor. — The rotation of 
crops should be planned so that an even distribution 
of farm labor is secured. The importance of this 
principle is so plain that its discussion is unnecessary. 
It is a topic outside of the domain of chemistr}^, 
but is nevertheless one of the most important to con- 
sider in economic farming, and should not be lost 
sight of in planning rotations. 

316. Economic Use of Manures. — Farm manure 
should be applied to those crops w^hich experience has 
shown to be the most benefited by its use. At least 
once during a five years' rotation the land should receive 
a dressing of stable manure. If commercial fertilizers 
are used, they should be applied to the crops which 
require the most help in obtaining food. With the 
growing of clover and the use of farm manures, only 
the poorer kinds of soil will require commercial fertil- 
izers for general crop production. It is more econom- 
ical to reenforce the farm manures with fertilizers 
especially adapted to the soil and crop than to purchase 
complete fertilizers. 

317. Salable Crops. — In all farming, something 
must be sold from the farm. It should be the aim to 



244 SOILS AND FERTILIZERS 

sell products which remove the least fertility, or if 
those are sold which remove large amounts, to return 
in cheaper forms the fertility sold. In a good rotation 
it is the plan to have at least one salable crop 
each year. The whole farm need not undergo the 
same rotation at the same time and the rotation may 
be subject to minor changes as circumstances require. 
To illustrate, wheat and flax occupy about the same 
position in a rotation. If when the crop is to be 
seeded the indications are that wheat will be a poor 
paying crop and flax sell well, flax should be sown. 
The rotation should be such that one of two or three 
crops may be grown as circumstances require. 

318. Rotations Advantageous in Other Ways. — A 

good rotation will be found advantageous in many 
ways. With one line of cropping, land becomes foul 
with special kinds of weeds which are unable to 
thrive when crops are rotated. Frequently the rota- 
tion must be planned so as to reclaim the land from 
weeds. 

Relief from insect pests is often secured by a proper 
rotation. Many insects are capable of living only on 
a special crop and when this crop is grown continually 
on the same land the best conditions for insect ravages 
exist. 

319. Long- and Short-course Rotations. — Rota- 
tions vary in length from 2 to 1 7 years. Long-course 



ROTATION OF CROPS 245 

rotations are more generally followed in European 
countries. The length of the rotation can only be de- 
termined by the conditions existing in different local- 
ities. As a general rule long-course rotations should 
be attempted only after a careful study of all the 
conditions relating to the system of farming that it is 
desired to follow. For northern latitudes a rotation 
of four or five years gives excellent results. In some 
localities three-course rotations are the most desirable. 

A rotation that is suitable for one locality or kind 
of farming may be unsuited for other localities or con- 
ditions. Because of variations in soil, climate, and 
rainfall, no definite standard rotation can be pro- 
posed that will be suitable for all conditions. 

320. Example of Rotation. — In dealing with the 
subject of rotations it is best to take actual problems 
as they present themselves and plan rotations that will 
best meet all conditions. For example, a farm of 
160 acres is to be rotated with the main object of pro- 
ducing fodder for live stock, and a small amount of 
grain for sale. The following rotation has been pro- 
posed to meet such conditions. ^^ 





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248 SOILS AND FERTILIZERS 

The farm is divided into eight fields of 20 acres 
each ; seven fields are brought under the rotation, 
while one field is left free for miscellaneous purposes. 
Each year there are produced 20 acres of corn, 20 
acres of timothy and clover hay, 10 acres each of 
wheat and flax, 20 acres of barley, and five acres each 
of corn fodder, rye, peas, and potatoes, while 20 acres 
are reserved for pasture. The main income is derived 
from the sale of live stock and dairy products. 

Problems on Rotations 

1. Plan a rotation for general farming (160 acres), using the fol- 
lowing crops: clover, timoth}-, barley, oats, potatoes, and corn. The 
soil is in an average state of fertility. Twenty -five head of stock 
are kept. 

2. Plan a three-course rotation for a sandy soil, the main object 
being potato culture. 

3. Plan a seven-year rotation for grain farming, using manure 
and sodium nitrate once during the rotation. The soil is a clay 
loam in a good state of fertility. 

4. Plan a rotation for general farming on a sandy loam. 

5. How would you proceed to bring an old grain farm from a low 
to a high state of productiveness? Begin with the feeding of the 
stock. 

6. Using commercial and special-purpose manures, how would 
you proceed to raise wheat, potatoes, and hay, each continuously? 

7. Plan a rotation for a northern latitude, where corn cannot be 
grown, and where clover and timothy fail to do well; wheat and all 
small grains thrive ; also millet, peas, rape, and some of the root 
crops. The soil is a clay loam, resting on a marl subsoil. Manure 
is very slow in decomposing. The rotation should be suited to 
general farming, wheat being the important market crop. 



CONSERVATION OF FERTILITY 

321. Manures Necessary for Conservation of Fer- 
tility. — In order to conserve the fertility of the soil, 
not only must a systematic rotation be practiced, but 
a proper use must be made of the crops produced. 
When they are sold from the farm and no restoration 
is made soils are gradually depleted of their fertility. 
No soil has ever been found that will continue to pro- 
duce crops without the use of manures. Many prairie 
soils give large yields for long periods without manur- 
ing, but they are never able to compete in productive- 
ness with similar soils that have been systematically 
cropped and manured. With a fertile soil the decline 
of fertility is so gradual that it is not observed unless 
careful records are kept of the yields from year to year. 

322. Use of Crops. — The use made of crops whether 
as food for stock or sold directly from the farm, deter- 
mines the future crop-producing power of the soil. 
With different systems of farming different uses are 
made of crops. When exclusive grain farming is fol- 
lowed no restoration of fertility is made, while in the 
case of stock farming, the manure produced contains 
fertility in proportion to the crops consumed. If 
good care is taken of the manure, and in place of the 
grains sold, mill products are purchased and fed, there 
is no loss of fertility. Between these two extremes, 
exclusive grain farming and stock farming, there are 
found in actual practice, different systems of farming, 



250 SOILS AND FERTILIZERS 

which remove various amounts of fertility from the 
soil. 

323. Two Systems of Farming Compared. — The 
losses of fertilit}' from farms are determined by the 
crops and products sold, the care of the manure, and 
the fertility in the products purchased and used on the 
farm. If an account were kept of the income and 
outgo of the fertility of farms it would be found that 
with some systems, the soil is gaining in fertility, while 
with others a rapid decline occurs. In studying the 
income and outgo of fertility, it is necessary to calcu- 
late the amount of the three principal elements, nitro- 
gen, phosphoric acid, and potash in the crops and 
products sold. For making these calculations tables 
are given in Sections 178 and 290. In the handling of ma- 
nure it is impossible to prevent losses, but it is possible 
to reduce them to very small amounts. Hence in the 
calculations, a loss of 3 per cent, is allowed for mechan- 
ical waste, and for uneven distribution of the manure; 
that is, in addition to the fertility sold from the farm a 
loss of 3 per cent, is allowed for all crops raised and 
consumed as food by stock. 

On one farm the crops raised and sold are : Flax 40 
acres, wheat 50 acres, oats 20 acres, barley 50 acres ; 
no stock is kept, the straw is burned, and the ashes 
are wasted. 



CONSERVATION OF FERTILITY 25 1 

ExcivUSivE Grain Farming. 
Sold from the Fartn 

Phosphoric 
Nitrogen. acid. Potash. 

Pounds. Pounds. Pounds. 

Flax, 40 acres- 1600 600 800 

Flax straw 600 120 320 

Wheat, 50 acres 1250 625 350 

Wheat straw 500 375 1400 

Oats, 2c acres 700 240 200 

Oat straw 300 1 20 700 

Barley, 50 acres 1400 750 400 

Barley straw 600 250 1500 

Total 6950 30S0 5670 

In addition to the nitrogen removed in the crops 
other losses must be considered. Experiments have 
shown that when exchisive grain farming is practiced, 
for every pound of nitrogen removed in the crop, four 
pounds are lost from the soil in other ways. This 
would make the total loss of nitrogen over 28,500 
pounds or 177 pounds per acre, which large as it may 
seem is the actual loss from the soil when grain only 
is raised and sold. Experiments at the Minnesota 
Experiment Station have shown that after a soil had 
been cultivated 40 years, the annual loss per acre of 
nitrogen in exclusive w^heat raising w^as 25 pounds 
through the crop and 146 pounds due to the oxidation 
of the nitrogenous humus of the soil.'^ 

When exclusive grain farming is followed, the 
annual losses of fertility from a farm of 160 acres are 
28,500 pounds of nitrogen, 3000 pounds of phosphoric 
acid, and 5500 pounds of potash. 



252 



SOILS AND FERTILIZERS 



On a similar farm of i6o acres the crops are rotated 
as described in Section 320. The amounts of fertility 
in the products sold, the crops raised and consumed 
as fodder, and the food and fuel purchased, are given 



in the following table : 



Stock Farming 
Sold from the Farm 

Phosphoric 

Nitrogen. acid. 

Pounds. Pounds. 

Butter, 5000 pounds 5 5 

Young cattle, 10 head 200 190 

Hogs, 20 of 250 pounds each. 100 40 

Steers, 2 48 38 

Wheat, 10 acres 250 125 

Flax, 10 acres 390 150 

Rye, 10 acres 285 128 

Total 1278 676 

Raised and Consumed on the Farm 

Clover, 20 tons 66 270 

Timothy, 20 tons 600 180 

Corn, 20 acres 1500 300 

Corn fodder, i acre 75 15 

Mangels, 2 acres 150 70 

Potatoes, I acre 40 20 

Straw, 40 tons 400 200 

Peas, 5 acres 85 

Oats, 20 acres 700 240 

Barley, 20 acres with straw- . 800 400 

4265 1780 
Mechanical loss of food con- 
sumed, 3 per cent 128 53 



Potash. 
Pounds. 

5 

16 

10 

4 

70 
190 

85 

380 



600 
800 
800 
60 
300 

75 

1000 

200 

200 

760 



4795 
144 



CONSERVATION OF FERTILITY 253 

Food and Fuel Purchased 

Phosphoric 

Nitrogen. acid. Potash. 

Pounds. Pounds. Pounds. 

Bran, 5 tons 275 260 150 

Shorts, 5 tons 250 150 100 

Oil meal, 2 tons 100 35 25 

Hard-wood ashes 25 100 

625 470 375 

Sold from farm 1278 676 380 

Lossinfoodconsumed,etc. . . . 128 53 144 

Total 1406 729 524 

Food and fuel purchased 625 470 375 

Balance lost from farm 781 259 149 

The manure produced and used on this farm results 
in the production of larger crop yields than is the 
case with exclusive grain culture. The clover and 
peas more than balance the loss of nitrogen. Ex- 
periments have shown that a rotation similar to 
this caused an increase in soil nitrogen. Manure, 
meadow and pasture all _ tend to increase the soil 
humus and nitrogen. The losses of phosphoric acid 
and potash are exceedingly small, averaging less 
than a pound per acre of each. The action of manure 
on this farm is continually bringing into activity the 
inert plant food of the soil so that ever\' year there is 
a larger amount of active plant food, which results in 
producing larger yields per acre. 

The increase or decrease of fertility on farms has 
a marked effect upon crop yields. For example the 



254 SOILS AND FERTILIZERS 

average yield of wheat in those counties in Minnesota 
where live stock is kept, is 7 bushels per acre greater 
than in similar counties where all grain farming is 
followed. 

Problems 

Calculate the income and outgo of fertility from the following 
farms : 

1. Sold from the farm : wheat 40 acres, oats 40 acres, barley 40 
acres, rye 20 acres, flax 10 acres. The straw is burned and no use 
is made of any manures. 

2. Sold from the farm : wheat 20 acres, barley 20 acres, flax 5 
acres, 1000 pounds of butter, 10 hogs, and 10 steers. Purchased : 
Bran 3 tons, shorts 2 tons, oil meal i ton. Crops produced and fed 
on farm : Clover and timothy hay 40 tons, corn fodder 3 acres, corn 
10 acres, oats and peas 10 acres, roots i acre, millet i acre, and bar- 
ley 5 acres. 

3. Sold from the farm : Wheat 10 acres, sugar beets 5 acres, milk 
100,000 pounds, butter 500 pounds, 20 pigs, 6 head of young stock, 
2 acres of potatoes. Purchased : 5 tons of bran, 2 tons of oil meal, 
I ton of cottonseed meal, 15 cords of wood, i ton of acid phosphate, 
1000 pounds of potassium sulphate, and 500 pounds of sodium ni- 
trate. Raised and consumed on the farm : Corn fodder 15 acres, 
mangels i acre, peas and oats 5 acres, clover 20 tons, timothy 10 
tons, straw from grain sold, oats, 10 acres, corn 20 acres. 



REFERENCES 

1. Venable : Histor}- of Chemistry. 

2. Gilbert : Inaugural Lecture, University of Oxford. 

3. Liebig : Chemistn.- in Its Applications to Agriculture and 
Physiology. 

4. Gilbert: The Scientific Principles of Agriculture (Lecture). 

5. Minnesota Agricultural Experiment Station, Bulletin No. 30. 

6. Stockbridge : Rocks and Soils. 

7. Association of Official Agricultural Chemists, Report 1898. 
Note : — This sentence should read : A division has recently 

been suggested by Hopkins in which the square root of ten is 
taken as the constant ratio between the grade of soil particles. 

8. Maryland Agricultural Experiment Station, Bulletin No. 21. 

9. Osborne : Journal of Analytical Chemistry, Vol. II, Part 3. 

10. Wiley : Agricultural Analysis, Vol. I. 

11. Hellriegel : Calculated from Beitrage zu den Natur\vissen- 
schaft Grandlagen des Ackerbaus. 

12. King : Wisconsin Agricultural Experiment Station, Report 
1889. 

13. Unpublished results of author. 

14. King : Soils. 

15. Roberts : Fertility of the Land. 

16. Minnesota Agricultural Experiment Station, Bulletin No. 41. 

17. Minnesota Agricultural Experiment Station, Bulletin No. 53. 

18. Whitney : Division of Soils, U. S. Department of Agriculture, 
Bulletin No. 6. 

19. Merrill : Rocks, Rock-weathering and Soils. 

20. Miintz : Comptes Rendus de I'Academie des Sciences, CX 
(1890). 

21. Storer : Agriculture, Vol. I. 

22. Dyer : Journal of the Chemical Society, March, 1894. 

23. Goss : Association of Official Agricultural Chemists, Report 
1896. 



256 SOILS AND FERTILIZERS 

24. Peter : Association of Official Agricultural Chemists, Report 

1895. 

25. Loughridge : American Journal of Science, Vol. VII (1874). 

26. Hilgard : Year-book U. S. Department of Agriculture, 1895. 

27. Houston : Indiana Agricultural Experiment Stalion, Bulle- 
tin No. 46. 

28. Miilder : From Mayer : Lehrbuch der Agrikulturchemie, 2. 

29. Journal of the American Chemical Society, Vol. XIX, No. 9. 

30. Year-book U. S. Department Agriculture, 1895. 

31. Loughridge : South Carolina Agricultural Experiment Sta- 
tion, Second Annual Report. 

32. Association of Official Agricultural Chemists, Report 1893. 

33. Washington Agricultural Experiment Station, Bulletin No. 

13- 

34. Association of Official Agricultural Chemists, Report 1894. 

35. California Agricultural Experiment Station, Report 1890. 

36. Minnesota Agricultural Experiment Station, Bulletin No. 29. 

37. Minnesota Agricultural Experiment Station, Bulletin No. 47. 

38. Lawes and Gilbert : Experiments on Vegetation, Vol. I. 

39. Boussingault : Agronomie, Tome I. 

40. Atwater : American Chemical Journal, Vol. VI, No. 8 and 
Vol. VIII, No. 5. 

41. Hellriegel : Welche Stick stoff Ouellen stehen der Pflanze zu 
Gebote? 

42. Minnesota Agricultural Experiment Station, Bulletin No. 34. 

43. Warington : U. S. Department of Agriculture, Office of Ex- 
periment Stations, Bulletin No. 8. 

44. Hilgard : Association of Official Agricultural Chemists, Re- 
port 1895. 

45. Marchal : Journal of the Chemical Society (abstract), June, 
1894. 

46. Kiinnemann: Die Landwirthschaftlichen Versuchs-Stationen, 
50(1898). 

47. Adametz : Abstract, Biedermann's Centralblatt fiir Agrikul- 
turchemie, 1887. 

48. Atwater: American Chemical Journal, Vol. IX (1887). 



REFERENCES 257 

49. Stutzer : Biedermann's Centralblatt fiir Agriculturchemie. 
1883. 

50. Jenkins : Connecticut State Agricultural Experiment Sta- 
tion, Report 1893. 

51. Wagner : Biedermann's Centralblatt fiir Agrikulturchemie, 
1897. 

52. Journal of the Royal Agricultural Society, 1850. 

53. From Sachsse : Lehrbuch der Agrikulturchemie, 

54. Lawes and Gilbert : Experiments with Animals. 

55. Beal : U. S. Department of Agriculture, Farmers' Bulletin 
No. 21. 

56. Minnesota Agricultural Experiment Station, Bulletin No. 26. 

57. Mainly from Armsby : Pennsylvania Agricultural Experi- 
ment Station, Report 1890. Figures for grains calculated from 
original data. 

58. Heiden : Dungelehre. 

59. Liebig : Natural Laws of Husbandry. 

60. Cornell University Agricultural Experiment Station, Bulle- 
tins Nos. 13, 27, and 56. 

61. Kinnard : From Manures and Manuring by Aikman. 

62. Wyatt : Phosphates of America. 

63. Wiley : Agricultural Analysis, Vol. III. 

64. Goessmann : Massachusetts Agricultural Experiment Station, 
Report 1894. 

65. Connecticut (State) Agricultural Experiment Station, Bulle- 
tin No. 103. 

66. Goessmann : Massachusetts Agricultural Experiment Station, 
Report 1896. 

67. Wheeler : Rhode Island Agricultural Experiment Station, 
Reports 1892, 1893, etc. 

68. Boussingault : From Storer : Agriculture. 

69. Handbook of Experiment Station Work. 

70. New York (State) Agricultural Experiment Station, Bulle- 
tin No. 108. 

71. Voorhees : U. S. Department of Agriculture, Farmers' Bulletin 
No. 44. 



258 SOILS AND FERTILIZERS 

72. Liebig : Die Chemie in ihrer Anwendung auf Agrikultur 
tind Physiologic. 

73. Warington : Chemistry of the Farm. 

74. Lawes and Gilbert : Growth of Wheat. 

75. Lawes and Gilbert : Growth of Barley. 

76. Lugger : Minnesota Agricultural Experiment Station, Bulle- 
tin No. 13. 

77. Lawes and Gilbert : Growth of Potatoes. 

78. Minnesota Agricultural Experiment Station, Bulletin No. 56. 

79. Shaw: U. S. Department of Agriculture, Farmers' Bulletin 
No. II. 

80. White : U. S. Department of Agriculture, Farmers' Bulletin 
No. 48. 

81. Lawes and Gilbert : Permanent Meadows. 

82. Thompson : Graduating Essay, Minnesota School of Agricul- 
ture, 

83. Nefedor : Abstract, Experiment Station Record, Vol. X, No. 4. 



EXPERIMENTS 

1. Pulverized Rock and Soil. — Pulverize in an iron mortar, 
pieces of feldspar, mica, granite, and limestone. Examine each 
with a lens. Finally mix all of the pulverized material, and com- 
pare the mixture with samples of soil. 

2. Weight of Soils. — Weigh a cubic foot of air-dried sand, clay, 
and peat. For this purpose use a box holding X of a cubic foot of 
soil. Do not compact the soil. 

3. Form of Soil Particles. — Examine under a microscope soil 
particles and distinguish the various grades of sand and silt. Ob- 
serve the form of the soil particles and make drawings of them. 

4. Separation of Soil Particles. —By means of sieves, with holes, 
1, Yz, and % mm. in diameter, separate these three grades of parti- 
cles as described in Section 10. To what type does the soil 
examined belong? 

5. Capillarity. — Place small glass tubes of various sizes in a 
vessel of water and note the height to which water rises by capil- 
larity. 

6. Capillarity of Soils. — Fill glass tubes 2 inches in diameter 
with clay and fine sand, respectively. Support the tubes so that 
one end wall touch the water in a cylinder. Obser\'e the rate and 
height to which the capillary water rises, making daily measure- 
ments for a week. 

7. Hydroscopic Moisture. — Place 5 grams of air-dried soil on a 
watch-glass, in a water-oven, and after two hours reweigh and de- 
termine the loss of weight. Calculate the per cent, of hydroscopic 
moisture. 

8. Influence of Cultivation on Soil Water. — Fill four boxes, each 
a foot square and a foot deep, with air-dried loam soil. Weigh the 
boxes and soil used. Each box is to be treated separately as fol- 
lows : Measure one-half gallon of water into a watering-pot. Allow 
the water from the watering-pot to flow on the soil, regulating the 
flow so that it is all absorbed. The soil should be saturated, but 



26o SOILS AND FERTILIZERS 

there should be no dripping. Measure or weigh an}' water left in 
the watering-pot. One box is to receive shallow surface cultivation, 
using for the purpose a small gardener's tool. Another box is to 
be left without receiving any treatment. The third is to receive 
treatment imitating that of the disk harrow, having the disks set per- 
pendicularly. A sharp knife may be used for this purpose. In the 
fourth box the disk cuttings are to be made at an angle. Leave 
each box exposed to the sun or in a heated room, and determine 
the loss of weight every day for a week. From the loss of weight, 
determine the per cent, of water lost and the per cent, left in the 
soil. 

9. Capacity of Soil to Absorb Water. — Weigh 100 grams of dry 
soil. Fit a medium-sized filter-paper in a funnel. Moisten the 
paper so that it will not absorb any more water. Then place the 
soil in the filter and add slowly from a beaker, containing exactly 
100 cc. of water, enough to thoroughly saturate the soil. Collect 
all of the drippings from the funnel. Measure the drippings and 
the unused water in the beaker. Calculate the per cent, of water 
absorbed by the soil. 

10. Capacity of Sand for Holding Water. — Repeat Experiment 9, 
using sand. 

11. The Influence of Manure upon the Water-holding Power of 
Soil. — Repeat Experiment 9, using 95 grams of sand and 5 grams 
of dry and finely pulverized manure. The sand and manure 
should be thoroughly mixed before performing the experiment. 

12. Action of Heat upon Soils. — Expose to the sun's rays samples 
of dry clay, peat, and sand ; after two hours' exposure, obtain the 
temperature of each. The bulb of the thermometer is simply cov- 
ered with soil. All of the observations should be made under sim- 
ilar conditions. 

13. Influence of Manure upon Soil Temperature. — Expose to the 
sun's rays, moist clay soil, and mixed clay and fresh horse manure. 
After two hours observe the temperature of each . 

14. Odor and Taste of Soils. — Observe the odor of dry, peaty 
soil that has been kept in a corked bottle. Note the taste of 



EXPERIMENTS 



261 



peaty and of alkaline soils ; test each \\4th moistened litmus paper. 

15. Absorption of Gases. — Put 50 grams of soil into a wide- 
mouthed bottle, add 50 cc. of water and i cc. strong ammonia. 
Note the odor. Cork the bottle, shake, and after twenty-four 
hours again observe the odor. 

16. Insoluble and Soluble Products of Soil. — Digest in a covered 
beaker 10 grams of soil with 100 cc. hydrochloric acid (50 cc. 
strong hydrochloric acid and 50 cc. water). After two hours' diges- 
tion, cool and filter, using 25 cc. water to wash the acid from the 
insoluble residue. Note the quantity and appearance of the insol- 
uble matter. To one-half the filtrate add ammonia until alkaline. 
What is the precipitate ? Remove it by filtering, and to this second 
filtrate add ammonium oxalate. What is the precipitate? 
Evaporate the remainder of the original filtrate nearly to 
dryness. Add 20 cc. water, 3 cc. nitric acid, and 5 cc. of 
ammonium molybdate. After shaking the test-tube con- 
taining the mixture, it is placed in a beaker of water and 
heated to about 65° C. What is the yellow precipitate ? 

17. Testing Soils for Combined Carbon Dioxide.— One 
gram of soil is placed in a test-tube (Fig. 35) and 5 cc. of 
water and 3 cc. of hydrochloric acid added. A small 
looped tube a, containing a drop of lime-water, is then 
inserted into the test-tube. The test-tube is warmed. 
Observe the precipitate formed in the loop. What is it ? 

18. Humus from Soils. —Five grams of soil are placed 
in a glass-stoppered bottle, 100 cc. water and 3 cc. hydro- 
chloric acid added. After shaking, the contents of the 
bottle are left twenty-four hours to subside. The acid 
is then poured off and 100 cc. of water added. The soil 
is left until the next day, when the water is poured off and 
100 cc. of water and 5 cc. of ammonia are added. After Fig. 35. 
shaking and allovi4ng a little time for the soil to settle, the ammo- 
nia solution is filtered off. 

To a portion of the filtrate add hydrochloric acid until the solu- 
tion is just acid. Observe the precipitate. Evaporate another por- 
tion of the solution to dryness. What is the black residue ? 



a 



6 



262 SOII^S AND FERTILIZERS 

19. The nitrogen of soils. — Place in a strong test-tube a mixture 
of 5 grams of soil and an equal bulk of soda-lime. Connect the 
test-tube with a delivery-tube which leads into another test-tube 
containing distilled water. Heat the test-tube containing the soil for 
five or ten minutes. Then test with litmus paper the liquid in the 
second test-tube, neutralize with standard acid as in Experiment 30. 

20. Nitrates. — Examine laboratory samples of the following 
nitrates : Potassium, calcium, and sodium. Place in separate test- 
tubes Yz gram of each, add 10 cc. of water, and heat gently. To 
each when cool add a few drops of sulphuric acid, then a few drops 
of an indigo solution. 

21. The Nitrogen of Blood. — Repeat Experiment 19, using 100 
milligrams of dried blood in place of the soil. 

22. Organic Nitrogen Soluble in Pepsin. — Prepare a pepsin solu- 
tion by dissolving 5 grams of commercial pepsin in a liter of water, 
adding i cc. of strong hydrochloric acid. Place in separate test- 
tubes 5 grams each of dried blood, tankage, and horn meal. Add 
25 cc. of pepsin solution and place the test-tubes in a cylinder con- 
taining water at a temperature of 40° C. Shake the test-tubes occa- 
sionally, and at the end of one-, two-, and five-hour periods observe 
the amounts of insoluble matter remaining in the test-tubes. 

23. Testing for Nitrates. — Dissolve some sodium nitrate, not 
exceeding 100 milligrams, in 10 cc. water. Add 2 cc. of a dilute 
solution of ferrous sulphate, and place the test-tube in a cylinder 
of water. Sulphuric acid is then added by means of a long stemmed 
funnel. Observe the dark ring formed. 

24. Water in Manure. — Dry 100 grams of fresh manure in a 
water-oven for four hours. Determine the loss of weight and the 
per cent, of water. 

25. Leaching Manure. — Place 5 kilos of manure, the same as 
used in Experiment 24, in a box provided with small holes in the 
bottom, so that the manure can be leached. Place the box over a 
sink or a receptacle for receiving the leachings. Percolate 3 gallons 
of water through the manure, daily, for five days. Finally weigh 
the manure, determine the per cent, of water, and the total loss of 
dry matter. 



EXPERIMENTS 263 

26. Volatilizing Ammonium Salts. — In separate test-tubes place 
about 100 milligrams each of ammonium carbonate and ammonium 
sulphate. Appl}^ heat gently and observe the results. Place a cold 
glass rod in the test-tube when the white fumes are being given off. 

27. Testing for Phosphoric Acid. — Dissolve a small piece of bone 
(5 grams) in 20 cc. nitric acid (10 cc. strong nitric acid and 10 cc. 
water). Filter. To the filtrate add 3 cc. of ammonium molybdate, 
warm, and shake. In a second test-tube dissolve 100 milligrams of 
sodium phosphate in 10 cc. water and add 3 cc. ammonium mo- 
lybdate. Compare the result with that obtained with the bone. 

28. Testing for Water-soluble and Acid-soluble Phosphates. — 
Place I gram of tricalcium phosphate in a test-tube wnth 10 cc. 
water. Boil. Filter through a close filter. To the filtrate add 3 cc. 
of ammonium molybdate. Repeat the experiment, using dilute 
nitric acid in place of water. Repeat the experiment, using mono- 
calcium phosphate and water. 

29. Preparation of Acid Phosphate. —Place 100 grams of pow- 
dered tricalcium phosphate in a large lead dish. Add slowly and 
vnth constant stirring 100 grams of commercial sulphuric acid, 
using an iron spatula for the purpose. Transfer the mixture to a 
wooden box and allow it to act for about three days. Then pul- 
verize and examine. The material is saved for Experiment 34. 
The mixing of the acid and phosphate should be done in a place 
where there is a good draft. 

30. Testing Ashes. — Test samples of leached and of unleached 
ashes in the way described in Section 240. 

31. Flocculation of Clay. — Ten grams of clay soil are placed in 
a tall beaker or cylinder, 1000 cc. of water added, and the material 
triturated. The water containing the suspended clay is divided 
into two portions. To one portion i gram of calcium carbonate is 
added and the mixture stirred. After two or three hours compare 
the two portions. 

32. Action of Lime on Acid Soil. — In a flask place 100 grams 
of acid peaty soil, add 5 grams of recently slaked lime and 200 cc. 
water ; connect the flask by means of a deliver\--tube with a wash- 
bottle containing lime-water and observe the results. 



264 SOILS AND FERTILIZERS 

33. MarL — Test a sample of marl for lime and carbon dioxide, 
as directed in Experiments 16 and 17. Observe the nature of the 
insoluble residue. Test the marl with litmus paper. 

34. Testing Land Plaster. — Test for carbon dioxide as directed 
in Experiment 17. There should be but little carbon dioxide in 
the best grades of land plaster. Digest i gram of gypsum in a test- 
tube with 10 cc. dilute hydrochloric acid. Observe the nature and 
the amount of insoluble matter. 

35. Mixing Fertilizers. — Mix in a large box 

200 grams acid phosphate (saved from 28), 
50 grams kainit, 
50 grams sodium nitrate. 
Calculate the approximate composition of this fertilizer and its 
trade value. 

36. Testing Fertilizers. — Test the above fertilizer for water- 
soluble phosphoric acid, as directed in Experiment 27. Test for 
nitrogen pentoxide, as directed in Experiment 19. 

37. Calculating Results. — A fertilizer is said to contain 3.1 per 
cent, ammonia, 12 per cent, bone phosphate of lime and 6 per cent, 
potassium sulphate ; calculate the equivalent amounts of nitrogen, 
phosphoric acid, and potash. 



REVIEW QUESTIONS 

I. From what are soils derived ? 2. What are the physical prop 
erties of soils ? 3. Why do soils differ in weight? Arrange clay 
sand, loam, and peat in order of weight per cubic foot. 4 When 
wet, what would be the order ? 5 . What is the absolute and what the 
apparent specific gravity of soils ? 6. Define the terms : Skeleton fine 
earth, fine sand, silt, and clay. 7. What are the physical properties 
of clay ? 8. What are the forms of the soil particles ? 9. How do 
different types of soil vary as to the number of soil particles per 
gram of soil ? 10. How is a mechanical analysis of a soil made ? 

11. Why do certain crops thrive best on definite types of soiP 

12. What factors must be taken into consideration in determining 
the type to which a soil belongs? 13. Explain the mechanical 
structure of a good potato soil. 14. How does a wheat soil differ in 
mechanical structure from a truck soil? 15. A good corn soil is 
also a good type for what other crops ? 16. How much water is re- 
quired to produce an average grain crop, and how do the rainfall 
and the water removed in crops during the growing season compare ? 
17. In what forms may water be present in soils ? 18. What is bot- 
tom water and when may it be utilized by crops ? 19. What is capil- 
lary water ? 20. Explain the capillary rnovement of water. 2 1 . Ex- 
plain how the capillary and non-capillan- spaces in the soil may be 
influenced by cultivation. 22. What is hydroscopic water and of 
what value is it to crops ? 23. What is peVcolation ? 24. To what 
extent may losses occur by percolation ? 25. What are the factors 
which influence evaporation ? 26. What is transpiration ? 27. In 
what three ways may water be lost from the soil ? 28. Why does 
shallow surface cultivation prevent evaporation ? 29. Why is it 
necessary to cultivate the soil after a rain ? 30. Explain the move- 
ment of the soil water after a light shower. 31. What influence 
has rolHng the land upon the moisture content of the soil ? 32, 
What IS subsoiling and how does it influence the moisture content 
of soils ? 33. What influence does early spring plowing exert upon 
the soil moisture ? 34. What is the action of a mulch upon the soil ? 
35. Why should different soils be plowed to different depths? 36. What 
IS meant by the permeabiHty of a soil ? 37. How may cultivation 
influence permeabihty? 38. How mav commercial fertilizers influ- 
ence the water content of soils ? 39. Explain the physical action 
of well-prepared farm manures upon the soil and their influence 
upon the soil water. 40. What is the object of good drainage? 
41- Why does deforesting a region unfavorably influence the agri- 
cultural value of a country ? 42. What are the sources of heat in 
soils ? 43. To what extent does the color of soils influence the tem- 



266 SOILS AND FERTILIZERS 

perature ? 44. What is the specific heat of soils ? 45. To what ex- 
tent does drainage influence soil temperature ? 46. How do 
manured and unmanured land compare as to temperature ? 47. 
What relation does heat bear to crop growth ? 48. What materials 
impart color to soils? 49. What is the effect of loss of organic 
matter upon the color of soils ? 50. What materials impart taste to 
soils ? Odor ? 51. What effect does a weak current of electricity 
have upon crop growth ? 52. Do all soils possess the same power 
to absorb gases? Why? 53. What is agricultural geology? 54. 
What agencies have taken part in soil formation ? 55. How does 
the action of heat and cold aid in soil formation ? 56. Explain the 
action of water in soil formation. 57. What is glacial action, and 
how has it been an important factor in soil formation ? 58. Ex- 
plain the action of vegetation upon soils. 59. How has the action 
of micro-organisms aided in soil formation ? 60. Explain the 
terms : Sedentary, transported, alluvial, colluvial, volcanic, and 
windformed soils. 61. What is feldspar and what kind of soil 
does it produce ? 62. Give the general composition of the follow- 
ing rocks and minerals and state the quality of soil which each 
produces: Granite, mica, hornblende, zeolites, kaolin, apatite, and 
limestone. 63. What elements are liable to be the most deficient 
in soils ? 64. Name the acid- and base-forming elements present 
in soils. 65. What are the elements most essential for crop growth ? 
66. State some of the different ways in which the elements present 
in soils combine. 67. Why is it customary to speak of the oxides of 
the elements and to deal with them rather than with the elements? 
68. Do the elements exist in the soil in the form of oxides? 69. 
What are double silicates ? 70. In what forms does carbon occur 
in soils? 71. Is the soil carbon the source of the plant carbon ? 
72. What can you say regarding the occurrence and importance of 
the sulphur compounds ? 73. What influence would o. 10 per cent, 
chlorine have upon the soil? 74. In what forms does phosphorus 
occur in soils? 75. What is the principal form in which the nitro- 
gen occurs in soils ? 76. What can be said regarding the hydrogen 
and oxygen of the soil? 77. State the principal forms and the 
value as plant food of the following elements : Aluminum, potas- 
sium, calcium, sodium, and iron. 78. For plant food purposes, 
what three divisions are made of the soil compounds ? 79. Why 
are the complex silicates of no value as plant food ? 80. Give the 
relative amounts of plant food in the three classes. 81. How is a 
soil analysis made? 82. What can be said regarding the economic 
value of a soil analysis? 83. What are some of the important facts 
to observe in interpreting results of soil analysis ? 84. Under what 
conditions are the results most valuable ? 85. Do the terms volatile 
matter and organic matter mean the same ? 86. How may organic 



REVIEW QUESTIONS 267 

acids be employed in soil analysis ? 87. Why are dilute organic 
acids used ? 88. Is the plant food equally distributed in both surface 
and subsoil ? 89. Do different grades of soil particles, from the 
same soil, have the same composition ? 90. What are " alkali 
soils"? 91. Why is the alkali sometimes in the form of a crust? 
92. Are all soils with white coating strongly alkaline? 93. Give 
the treatment for improving an alkali soil. 94. How^ may a small 
" alkali spot " be treated? 95. What are the sources of the organic 
compounds of soils? 96. How may the organic compounds of the 
soil be classified ? 97. Explain the term humus. 98. How is the 
humus of the soil obtained ? 99. What is humification ? W^hat is 
a humate ? How are humates produced in the soil ? 100. Explain 
how different materials produce humates of different value. loi. 
Arrange in order of agricultural value the humates produced from 
the following materials : Oat straw% sawdust, meat scraps, sugar, 
clover. 102. Of what value are the humates as plant food? 103. 
How much plant food is present in soils in humate forms? 104. 
What agencies cause a decrease of the humus content of soils ? 
105. To what extent does humus influence the physical properties of 
soils? 106. What is humic acid ? 107. What soils are most liable 
to be in need of humus ? When are soils not in need of humus ? 
108. In what ways does the humus of long-cultivated soils differ 
from that of new soils ? 109. How may different methods of 
farming influence the humus content of soils ? 1 10. What may be 
said regarding the importance of nitrogen as plant food? iii. 
What are the functions of nitrogen in plant nutrition? 112. How 
may the foliage indicate a lack or an excess of this element ? 113. 
In what three ways did Boussingault conduct experiments relating 
to the assimilation of the free nitrogen of the air ? 114. What were 
his results? 115. What conclusions did Ville reach? 116. Give 
the results of Eawes and Gilbert's experiments. 117. How did 
field results compare with laboratory- experiments? 118. In what 
ways w^ere the conditions of field experiments different from those 
conducted in the laboratory? 119. Give the results of Hellriegel's 
and Wilfarth's experiments. 120. What is noticeable regarding 
the composition of clover root nodules? 121. Of what agricultural 
value are the results of Hellriegel? 122. W^hat is the source of the 
soil's nitrogen ? 123. How may the organic nitrogen compounds 
of the soil vary as to complexity ? 124. To what extent may the 
nitrogen in soils vary ? 125. Tow-hat extent is nitrogen removed 
in crops ? 126. To what extent are nitrates, nitrites, and ammo- 
nium compounds found in soils ? 127. To what extent is nitrogen 
returned to the soil in rain-water. 128. How may the ratio of 
nitrogen to carbon vary in soils ? Of what agricultural value is this 
ratio ? 129. Under what conditions do soils gain in nitrogen con- 
tent? 130. W^hat methods of cultivation cause the most rapid de- 



268 SOILS AND FERTILIZERS 

cline in the nitrogen content of soils? 131. What is nitrification? 
132, What are the conditions necessary for nitrification? and 
what are the food requirements of the nitrifying organism ?' 133, 
W^hy is oxygen necessary for nitrification ? 134. How does tem- 
perature, moisture, and sunUght influence this process? 135. 
What part does calcium carbonate and other basic compounds take 
in nitrification ? 136. How is nitrous acid produced? 137. What 
is denitrification ? 138, W^hat other organisms are present in soils 
besides those which produce nitrogen pentoxide, nitrogen trioxide. 
and ammonia? 139. What chemical products do these various or- 
ganisms produce ? 140. Why are soils sometimes inoculated with 
organisms ? 141. Why does summer fallowing of rich lands cause 
a loss of nitrogen ? 142. What influence have deep and shallow 
plowing, and spring and fall plowing upon the available soil 
nitrogen ? 143. Into what three classes are nitrogenous fertilizers 
divided ? 144. How is dried blood obtained ? What is its compo- 
sition, and how is it vised ? 145. What is tankage ? How is it 
used, and how does it diff^er in composition from dried blood? 
146. What is flesh meal ? 147. What is fish scrap fertilizer, and 
what is its comparative value ? 148. What seed residues are used 
as fertilizer? What is their value? 149. What method is em- 
ployed to detect the presence of leather, hair, and wool waste in 
fertilizers? Why are these materials objectionable? 150. How 
may peat and muck be used as fertilizers? 151. What is sodium 
nitrate ? How is it used, and what is its value as a fertilizer? 152. 
How does ammonium sulphate, as a fertilizer, compare in value 
with nitrate of soda? 153. What is the difference between the 
nitrogen content and the ammonia content of fertilizers? 154. 
What is fixation ? Give an illustration. 155. To what is fixation 
due ? 156, W'hat part does humus take in fixation? 157. Why do 
soils differ in fixative power ? Why are nitrates not fixed ? 158. 
Why is fixation a desirable property of soils? 159. Why is it 
necessary to study the subject of fixation in the use of manures ? 
160. Why are farm manures variable in composition? 161. What 
is the distinction between the terms stable manure and farm-yard 
manure? 162. About what per cent, of nitrogen, phosphoric acid, 
and potash is present in ordinary manure? 163. Coarse fodders 
cause an increase of what element in the manure? 164. What four 
factors influence the composition and value of manure? 165. 
What influence do absorbents have upon the composition of 
manures? 166. What advantages result from the use of peat and 
muck as absorbents ? 167. Compare the value of manure produced 
from clover with that from timothy hay. 168. How may the value of 
manure be determined from the nature of the food consumed ? 
169. To what extent is the fertility of the food returned in the 
manure? 170. Is much nitrogen added to the body during the 



REVIEW QUESTIONS 269 

process of fattening? 171. Explain the course of the nitrogen of 
the food during digestion and the forms in which it is voided in 
the manure. 172. Compare the solid and liquid excrements as to 
constancy of composition and amounts produced. 173, What is 
meant by the manurial value of food ? 174. Name five foods with 
high manurial values ; also five \\4th low manurial values. 175. 
What is the usual commercial value of manures compared wdth 
commercial fertilizers? 176. How does the manure from young 
and from old animals compare as to value? 177. How much 
manure does a well-fed cow produce per day? 178. What are the 
characteristics of cow manure? How do horse manure and cow 
manure differ as to composition, character, and fermentability ? 
179. What are the characteristics of sheep manure? 180. How 
does hen manure differ from any other manure ? 181. W^hy should 
the solid and liquid excrements be mixed to produce balanced 
manure? 182. What volatile nitrogen compound may be given off 
from manure ? 183. What may be said regarding the use of human 
excrements as manure ? 184. Is there any danger of an immediate 
scarcity of plant food to necessitate the use of human excrements 
as manure? 185. To what extent may losses occur when manures 
are exposed in loose piles and allowed to leach for six months ? 
186. What two classes of ferments are present in manure? 187. 
Explain the workings of the tw^o classes of ferments found in 
manures. 188. How much heat may be produced in manure dur- 
ing fermentation ? 189. Is water injurious to manure? 190. How 
should manure be composted ? What is gained? 191. How does 
properly composted manure compare in composition with fresh 
manure? 192. Explain the action of calcium sulphate in the pre- 
servation of manure. 193. How does manure, produced in open 
barnyards, compare in composition with that produced in covered 
sheds? 194. When may manure be taken directly to the field and 
spread? 195. How may coarse manures be injurious to crops? 
196. What is gained by manuring pasture land ? 197. Is it econom- 
ical to make a number of small manure piles in a field ? Why ? 
198. At what rate per acre may manure be used? 199. To 
what crops is it not advisable to add stable manure ? 200. How 
do a crop and a manure produced from that crop compare in 
manurial value? 201. Why do manures have such a lasting effect 
upon soils? 202. Why does manure from different farms have 
such variable values and composition ? 203. In what seven ways 
may stable manures be beneficial ? 204. What may be said regard- 
ing the importance of phosphorus as plant food ? What function 
does it take in plant economy ? 205. How much phosphoric acid 
is removed in ordinary farm crops ? 206. To what extent 
is phosphoric acid present in soils? 207. What are the sources 
of the soil's phosphoric acid ? 208. What are the commer- 



270 SOIIvS AND FERTILIZERS 

cial sources of phosphate fertilizers ? 209. Give the four cal- 
cium phosphates and their relative fertilizer values. 210. Define 
reverted phosphoric acid. 211. Define available phosphoric acid. 
212. In what forms do phosphate deposits occur? 213. State the 
general composition of phosphate rock. 214. Explain the process 
by w^hich acid phosphates are made. Give reactions. 215. How 
is the commercial value of phosphoric acid determined? 216. 
What is basic phosphate slag and what is its value as a fertilizer ? 
217. What is guano? 218. How do raw bone and steamed bone 
compare as to field value ? As to composition ? 219. What is dis- 
solved bone ? 220. How is bone-black obtained, and what is its 
value as a fertilizer? 221. How are phosphate fertilizers applied to 
soils? In what amounts? 222. How may the phosphoric acid of 
the soil be kept in available condition ? 223. What is the function 
in plant nutrition of potassium? 224. To what extent is potash 
removed in farm crops ? 225. To what extent is potash present in 
soils? 226. What are the sources of the soil's potash? 227. What 
are the various sources of the potash used for fertilizers? 228. 
What are the Stassfurt salts, and how are they supposed to have 
been formed? 229. What is kainit ? 230. How much potash is 
there in hard-wood ashes ? 231. In what ways do ashes act on soils ? 
232. How do unleached ashes differ from leached ashes? 233. 
What is meant by the alkalimetry of an ash? 234. Of what value, 
as fertilizer, are hard- and soft-coal ashes? 235. What is the fer- 
tilizer value of the ashes from tobacco stems? 236. Cottonseed 
hulls? 237. Peat-bog ashes? 238. Saw-mill ashes? 239. Lime- 
kiln ashes? 240. How is the commercial value of potash deter- 
mined? 241. How are potash fertilizers used? 242. Why is it 
sometimes necessary to use a lime fertilizer in connection with a 
potash fertilizer ? 243. What can be said regarding the importance 
of lime as a plant food ? 244. To what extent is lime removed in 
crops? 245. To what extent do soils contain lime ? 246. What are 
the lime fertilizers ? 247. Explain the physical action of lime fer- 
tilizers. 248. Explain the action of lime on heavy clays. 249. On 
sandy soils. 250. In what ways, chemically, do lime fertilizers 
act? 251. How may lime aid in liberating potash? 252. What is 
marl? 253. How are lime fertilizers applied? 254. What is the 
result when land plaster is used in excess? 255. Explain the 
action of salt on soils ? 256. When would it be desirable to use 
salt as a fertilizer? 257. Is soot of any value as a fertilizer? Ex- 
plain its action. 258. Are sea-weeds of any value as fertilizer? 259. 
What is a commercial fertilizer ? An amendment ? 260. To what 
does the commercial fertilizer industry owe its origin? 261. Why 
are commercial fertilizers so variable in composition? 262. Ex- 
plain how a commercial fertilizer is made. 263, Why are the 
analysis and inspection of fertilizers necessary ? 264. What are the 



REVIEW QUESTIONS 271 

usual forms of nitrogen in commercial fertilizers ? 265. Of phos- 
phoric acid and potash? 266. How is the value of a commercial fer- 
tilizer determined ? 267. What is gained by home mixing of fer- 
tilizers ? 268. What can be said about the importance of tillage 
when fertilizers are used? 269. How are commercial fertilizers 
sometimes injudiciously used? 270. How may field tests be con- 
ducted to determine a deficiency in available nitrogen, phosphoric 
acid, or potash? 271. To determine a deficiency of two elements? 
272. How are the preliminary results verified? 273. Why is it 
essential that field tests with fertilizers be made? 274. Under what 
conditions does it pay to use commercial fertilizers? 275. What is 
the result when commercial fertilizers are used in excessive 
amounts? 276. Under ordinary conditions, what special help do 
the following crops require : Wheat, barley, corn, potatoes, man- 
gels, turnips, clover, and timothy? 277. In what ways do commer- 
cial fertilizers and farm manures differ? 278. Does the amount of 
fertility removed by crops indicate the nature of the fertilizer re- 
quired? In what ways are plant ash analyses valuable ? 279. Ex- 
plain the action of plants in rendering their own food soluble. 280. 
Why do crops differ as to their power of procuring food? 281. 
Why is wheat less liable to need potash than nitrogen? 282. What 
position should wheat occupy in a rotation? 283. In what ways do 
wheat and barley differ in feeding habits? 284. What can be said 
regarding the food requirements of oats? 285. Corn removes from 
the soil twice as much nitrogen as a wheat crop, yet a wheat crop 
usually thrives after a corn crop. Why? 286. W^hat help is corn 
most liable to need in the way of food? 287. What position should 
flax occupy in a rotation? 288. On what soils does flax thrive best? 
289. What is the essential point to observe in the manuring of po- 
tatoes? 290. W^hat kind ot manuring do sugar-beets require? 291. 
Why should the manuring of mangels be different from that of tur- 
nips? 292. What may be said regarding the food requirements of 
buckwheat and rape? 293. W^hat kind of manuring do hops and 
cotton require? 294. What kind of manuring is most suitable for 
leguminous crops? 295. What is the object of rotating crops? 296. 
Should the whole farm undergo the same rotation system? 297. 
What is meant by soil exhaustion? 298. What are the nine impor- 
tant principles to be observed in a rotation? 299. Explain why it 
is essential that deep and shallow rooted crops should alternate. 
300. Why is it necessary that the humus be considered in a rota- 
tion? 30 1 . What is the ob j ect of gro\\4ng crops of dissimilar feeding 
habits? 302. How may crop residues be used to the best advantage? 
303. In what ways may a decline of soil nitrogen be prevented by 
a good rotation of crops? 304. In what ways do different crops and 
their cultivation influence the mechanical condition of the soil? 
305. How may the best use be made of the soil water? 306. How 



272 SOILS AND FERTILIZERS 

may a rotation make an even distribution of farm labor? 307. How 
are manures used to the best advantage in a rotation? 308. In what 
other ways are rotations advantageous? 309. What may be said re- 
garding long- and short-course rotations? 310. How is the conser- 
vation of fertilitv best secured? 311. Why does the use made of 
crops influence fertility? 312. W^hat are the essential points to be 
observed in the two systems of farming compared in Section 323? 
313. Is it essential that all elements removed in crops should be re- 
turned to the soil in exactly the amounts contained in the crops? 
Why? 314. How does manure influence the inert matter of the 
soil? 315. What general systems of farming best conserv-e fertility? 
316. Under what conditions may farms be gaining in reserve fer- 
tilit}'? 317. Why in continued grain culture does the loss of nitro- 
gen from a soil exceed the amount removed in the crop? 



CORRECTIONS 

Page 25, line 19, for "three months," read "two months." 

Page 28, line 18, after soil, add : "absorbed from the air." 

Page 28, line 26, add : "when reduced below 4 per cent." 

Page 64, Hue 5, for "one-half," read "one-tenth." 

Page 72, line 18, read"94," not "96." 

Page 150, line 2, read "clover hay nitrogen, 35," not "45." 

Page 187, under Flax, transpose "19" and "8." 



INDEX 



Absorbents 143 

Absorption of heat by soils 42 

Absorptive power of soils 46 

Acids in plant roots 228 

Aerobic ferments 121, 158 

Agricultural geology 49 

Agronomy 9 

Albite . . .'. 56 

Alkaline soils 87 

Aluminum of soils 66 

Amendments 205 

Ammonium compounds 115 

salts 136 

Anaerobic ferments 159 

Analysis of soil, how made.. 73, 74 

of soil, value of 76, 80 

Apatite rock 58 

Application of fertilizer 222 

of manures 163, 165 

Arrangement of soil particles 16 

Ashes 191 

action of, on soils 192 

testing of 1 93 

Assimilation of nitrogen 102 

of phosphates 173 

Atmospheric nitrogen 104 

Atwater 108, 132 

Availability of plant food 79 

Available phosphates 177, 184 

nitrogen 113, 133 

Barle}^ fertilizers for 223 

food requirements of 231 

Blood, dried 1 28 

Bone, dissolved 183 

fertilizers 18 r 

Boneash 182 

Bone-black 183 

Boussingault's experiments 

4, 104, 105, 106 



Calcium an essential element . . 196 
carbonate and nitrific'on - 123 

compounds of soils 67 

phosphate 58, 1 75 

Capillarity 27 

and cultivation 31 

Carbon of soil 63 

sources for plant growth . .63 

Chlorine of soil 64, 87 

Cla}', formation of 58 

particles 13 

Clover as manure 134 

nitrogen returned by 

108, 118, 253 

root nodules no 

manuring of. 194, 199, 224,237 

Coal ashes 193 

Color of plants, influence(i by 

nitrogen 1 104 

of soils 45 

Combination of elements in soils. "61 

Commercial fertilizers 205, 225 

and tillage 216 

abuse of 216 

extent of use 205 

field tests with 218 

home mixing of 214 

inspection of 209 

mechanical condition of .210 

nitrogen of 210 

phosphoric acid of 211 

potash of 212 

proper use of 217 

valuation of 213 

Composition of soils 83, 85 

Composting manures 160 

Corn , fertilizers for 223 

food requirements of 232 

and manure 167 

Cotton, fertilizers for 235 



274 



INDEX 



Cottonseed meal 132 

Cow manure 152 

Crop residue 239 

Cultivation after rains 33 

shallow surface 31 

Da v}', work of 3 

Dissolved bone 1 83 

Distribution of soils 54 

Denitrification 123 

De Saussure, work of 3, 104 

Drainage 41, 43 

Dried blood 1 28 

Dyer 80 

Early truck soils 19 

Electricity of soil 47 

Evaporation 30 

Excessive use of fertilizers 222 

Experiments 259 

Fallow fields 126 

Fall plowing 35 

Farm manures 141, 171 

Farm manures and commercial 

fertilizers 224 

Feldspar 55, 209 

Fermentation of manures 158 

Fertility, conservation of 249 

removed in crops 227 

Fertilizers, amount to use 222 

influence upon soil water. 39 

on barley 231 

on wheat 230 

Field tests with fertilizers 218 

Fine earth 12 

Fish fertilizer 132 

Fixation 1 38 

Flax, food requirements of 233 

soils 20 

Flesh meal 131 

Forest fires 97 

Formaiion of soils 49, 54 

Form of soil particles 14 

Fruit soils 20 



Gains of humus 100 

of nitrogen 117 

Glaciers, action of 51 

Grain soils 22 

Granite 58 

Grass lands, fertilizers for 236 

Grass soils 22 

Guano 181 

G3'psum and manure 161 

Heat and crop growth 44 

produced by manures 160 

of soil 4 2, 43 

Heiden 156, 161 

Hellriegel 25, 30, 109 

Hen manure 154 

Hog manure 154 

Hops, fertilizers for 236 

Horse manure 152 

Human excrements 156 

Humates 91 

as plant food 95 

Humification 92 

Humic acid 98 

Humic phosphates 92 , 1 84 

Humus 91 

active and inactive 100 

causes fixation 139 

composition of 94 

Income and outgo of fertility.. 

250, 253 

Injurv of coarse manures ..40, 164 

Insoluble matters of soils 70, 71 

Iron compounds of soil 68 

Kainit 190, 206, 212 

Kaolin 58 

Ki"g 32, 35, 36 

Lawesand Gilbert.. 7, 107, 229. 230 

Leached ashes 192 

Leaching of manure 157 

Leather 133 

Leguminous crops,fertilizers for, 237 
as manure 134 



INDEX 



275 



Liebig 6, 7, 156, 227 

Liquid manure 147 

lyime, action on soils 198 

amount of, in soils 197 

amount removed in crops. 197 

excessive use of 201 

fertilizers 196 

indirect action of 199 

physical action of •• 201 

use of 201 

and acid soil 198 

and clover 199 

Loam soils 24 

Loss of fertility in grain farming, 252 

Loss of humus 97 

of nitrogen 117, 126 

Losses from manures 157, 158 



Magnesium compounds of soils. .68 

salts as fertilizers 202 

Mangels, fertilizers for 224 

Manure from cow 152 

hen 154 

hog 154 

horse 152 

sheep 153 

Manures, farm 141 

influenced by foods 144 

use of, in rotations 243 

value of 1 70 

and soil water 39, 98 

Manurial value of foods 149 

Manuring of crops 166 

pasture land 1 64 

Marl 200 

Mechanical analysis of soils 17 

condition of fertilizers- . .210 
Methods of farming, influence 

of, upon fertility 100 

Mica 57 

Micro-organisms and soil for- 
mation 49. 53 

Mixing manures 155 

Movement of water after rains. -33 
Mulching 36 



Nitrate of soda 135 

Nitric nitrogen 136 

Nitrification 119 

conditions necessary for 120 

and sunlight 122 

and plowing 127 

Nitrogen assimilation 104 

as plant food 102 

compounds of soil 65 

deficiency of, in soil 219 

losses of, from soil 117 

ratio of, to carbon 116 

removed in crops 114 

of commercial fertilizers. 2 10 

amount of, in soils 113 

as organic forms 112 

as nitrates 114 

availability of 113 

forms of 112 

origin of 1 1 1 

Nitrogenous manures 128 

Number of soil particles 17 

Odor of soils 46 

Organic acids, action of, upon 

soils 79, So 

Organic compounds of soil, 

classification of 90 

source of 90 

Organic nitrogen 128, 133 

Organisms, ammonia-producing, 1 23 

of soil 124 

nitrifying 1 20 

products of 125 

Osborne 18 

Orthoclase 56 

Oxidation in soil 43 

Peat 134, 144 

Percolation 28 

Permeability of soils 38 

Phosphate fertilizers 172 

use of 1 83 

rock 177 

slag 180 



276 



INDEX 



Phosphoric acid of commercial 

fertilizers 211 

acid in soils 174 

acid, deficiency of 220 

acid removed in crops 173 

Phosphorus compounds of soils. .64 

Physical property of soils 10, 47 

modified by farming 10 1 

Plant food, classes of 69, 70 

ash and fertilizers 226 

Plowing, depth of 37 

fall 35 

ppring :••. : 36 

influences nitrification. . . 127 

Potash fertilizers 1S6 

fertilizers, use of 194 

of commercial fertilizers. 212 

in soils 188 

in soils, sources of 188 

removed in crops 187 

and lime, joint use of 194 

Potassium compounds of soil ... 67 

Potato, fertilizers for 224 

food requirements of .... 233 
soils 19 

Questions 265 

Rainfall and crop production ... 25 

Rape, food requirements of 235 

References 255, 257 

Reverted phosphoric acid 1 76 

Roberts 37, 157 

Rocks, composition of 55,59 

Rock disintegration 49 

Rolling 34 

Roots, action on soil 228 

Rotation of crops 238, 254 

of crops, principles in- 
volved 239 

length of 244 

problems 248 

and farm labor 243 

and humus 241 

and insects 244 

and soil nitrogen 241 



Rotation and soil water 242 

and weeds 244 

Salt as a fertilizer 202 

Sand, grades of 13, 14 

Seaweeds as fertilizers 203 

Sedentary soils 54 

Seed residues 132 

Sheep manure 153 

Silicon and silicates 163 

Silt particles 14 

Size of soil particles 12 

Skeleton of soils 12 

Small manure piles 165 

Sodium compounds of soil 68 

Soil, composition of 83, 85 

exhaustion 238 

types 19 

Soot 203 

Specific gravity of soil 12 

Spring plowing 36 

Stockbridge 12, 25 

Stock farming and fertility 254 

Storer 63, 1 29 

Stutzer 133 

Sub-soiling 35 

Sugar beets, fertilizers for 234 

beet soils 21 

beets and farm manures. .167 

Sulphate of potash 190 

Sulphur compounds of soil' 64 

Superphosphates 178 

Tankage 130 

Taste of soils 46 

Temperature of soils 42 

Tests with fertilizers 218 

Thaer, work of 3 

Tobacco, manuring of 167 

Tobacco stems 193 

Transported soils 54 

Truck farming and fertilizers ..221 
Turnips, fertilizers for 224 

Ville 107 

Volcanic soils 55 



INDEX 



277 



Volume of soils 12 

Voorhees 214 

Water, action of, upon rocks and 

soils 50 

bottom 26 

capillary 27 

capillary, conservation of 

31, 32, 33 

hydroscopic 28 

losses by evaporation 30 

losses by transpiration 30 

of soil 26, 41 

of soil influenced — 

by drainage 41 

plowing.. 35, 36 
forest regions, 4 1 
manures. .39, 98 



Water of soil influenced — 

by mulching. • • .36 

rolling 34 

subsoiling • ••35 

required by crops 25 

Warington 119,121,123,229 

Weeds, fertility in 203 

W^eight of soils 11 

W^heat, fertilizers for 223 

food requirements of 229 

soils 22,23. 

Whitney 17, 47 

Wilfarth 109 

Wood ashes 191 

Wool waste 204 

Zeolites 57, 139 



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Special Methods of Analysis of Ores and Furnace Products. 
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mittee of the Chemical Section, Engineers' Society of Western 
Pennsylvania . . - - Paper, $ .75 ; cloth, $1.00 

HARDY. 

Elements of Analytic Geometry. — By Joseph Johnston 
Hardy, Professor of Mathematics and Astronomy in Lafay- 
ette College - - - - - - - - $2.00 

The book contains all the matter ordinarily required for the 
mathematical courses of our best schools and colleges. The mat- 
ter is so put upon the page as to make the reading of the book as 
easy and pleasant as possible. The figures are numerous, clear, 
and beautiful. The authority is required for every step taken. 
The demonstrations are so drawn up as to train the student in the 
orderly and logical construction of an argument. The language is 
«o chosen as to train the student in the clear, correct, and forceful 
expression of thought. Indeed the chief object of the book is to 
train the critical faculty and give skill in the arts of thinking and 
expressing thought. 



The Chemical Publishing Company, 

EASTON, PENNA. 



J 



JUL 10 my 



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